For how many of the five neighborhoods did the ratio of the foreign-born population to the total population of the neighborhood increase from 1930 to 1990?

• A. Three
• B. One
• C. Four
• D. None
• E. Two

Recent research has questioned the long-standing view of pearly mussels as exclusively suspension feeders (animals that strain suspended particles from water) that subsist on phytoplankton (mostly algae). Early studies of mussel feeding were based on analyses of gut contents, a method that has three weaknesses. First, material in mucus-bound gut contents is difficult to identify and quantify. Second, material found in the gut may pass undigested out of the mussel, not contributing to its nutrition. Finally, examination of gut contents offers limited insight into the mechanisms and behaviors by which mussels acquire food. Modem studies suggest that pearly mussels feed on more than just algae and may use other means than suspension feeding. Pedal feeding (sweeping up edible material with a muscular structure called the foot) has been observed in juvenile pearly mussels.
Besides the phytoplankton pearly mussels capture from the water column, their guts also contain small animals, protozoans, and detritus (nonliving particulate organic material). Recent studies show that mussels can capture and assimilate bacteria as well, a potentially important source of food in many fresh waters.
Another potential source of food for mussels is dissolved organic matter. Early studies showing that pearly mussels could take up simple organic compounds were largely discounted because such labile (unstable) compounds are rarely abundant in nature. Nevertheless, recent work on other bivalves suggests that dissolved organic matter may be a significant source of nutrition.
Of this complex mix of materials that pearly mussels acquire, what is actually required and assimilated?
Stable-isotope analyses of mussels taken from nature and of captive-reared mussels are beginning to offer some insight into this question. Nichols and Garling showed that pearly mussels in a small river were omnivorous, subsisting mainly on particles less than 2S micrometers in diameter, including algae, detritus, and bacteria. Bacterially derived carbon was apparently the primary source of soft-tissue carbon. However, bacteria alone cannot support mussel growth, because they lack the necessary long-chain fatty acids and sterols and are deficient in some amino acids. Bacteria may supplement other food resources, provide growth factors, or be the primary food In habitats such as headwater streams, where phytoplankton is scarce. Juvenile mussels have been most successfully reared m the laboratory on diets containing algae high in polyunsaturated fatty acids. Thus, it appears that the pearly mussel diet in nature may consist of algae, bacteria, detritus, and small animals and that at least some algae and bacteria may be required as a source of essential biochemicals.
The primary purpose of the passage is to

• A. suggest that a particular source of nutrients is more essential to pearly mussels than was previously thought
• B. explain why evidence used to support a long-standing view about pearly mussels is flawed
• C. summarize the present state of knowledge about what pearly mussels eat
• D. contrast two mechanisms by which pearly mussels have been shown lo feed
• E. question whether research findings about laboratory-reared pearly mussels can be extrapolated to pearly mussels in natural habitats

A certain train will travel from City A to City B. and then back to City A along the same route. The train is scheduled to spend a total of T hours traveling lime for the round-trip. The train travels from City A to City B in 13 hours, traveling at an average speed of 25 miles per hour. If the train is to arrive exactly on schedule, at what average speed must the train travel from City B to City A ?

• A.
  
• B.
  
• C.
  
• D.
  
• E.
  

A health club lias SOO members. 175 of whom exercised last Friday and 450 of whom exercised last Saturday. Of the members who exercised on at least one of the two days. 90 exercised both last Friday and last Saturday. Which of the following statements are true?

• A. More than 600 of the members exercised either last Friday or last Saturday or bom.
• B. More than 400 of the members exercised neither last Friday nor last Saturday.
• C. More than 300 of the members exercised last Saturday but not last Friday.