Snail populations are dying off in certain European forests because acid 4 q0 l! J8 v! m0 [. l' d: }* z
rain has depleted the soil of nutrients the snails need. These forests are * a5 G% g: v0 u# ?
the sole habitat of birds called passerines, which get most of the calcium 8 m: w5 t4 v. h P3 [
they need from snail shells. When passerines get too little calcium, more 2 Q2 D9 K- o% s
of their eggs have abnormally thin shells, and, accordingly, fewer off-- C6 t. U4 g7 f1 s5 G
spring survive. Therefore, acid rain will probably cause a decrease in 6 `1 G3 g( @1 a# p: Q6 e
the population of European passerines.
6 ?' s4 L' |" I2 E9 R# |) N Which of the following, if true, most strengthens the argument given?
/ I5 y3 ^/ F) c! P6 W A Nothing in the forests other than snail shells can provide passerines & R3 }5 U, ` |' Q: m
with calcium in the amount that they need.
) K- g2 t8 L( v B Some cases of passerines laying eggs with very thin shells have * }$ J5 E" E0 y+ {; X8 r" m8 X" e
been attributed to causes other than calcium deficiency. . A- ~. T# g0 Y% |
C When the population of passerines in a forest declines, populations
6 [, O/ z( W# S; b* h1 N* D4 c. } of predatory birds that prey on passerines also tend to decline in
8 ^# v: O1 l1 K) Q5 }0 \ that forest. $ `2 ~* m8 {% Y: a8 l Z7 f" i0 @
D If the acidity of rain in Europe were reduced, then nutrients in forest $ d" y a4 J" P% Z' ?0 @' F( h
soils would be restored to earlier levels.
* ]# W' v3 z+ f5 j E Because of recent expansion of certain European forests, the amount : m; I9 j/ ?* {0 j
of habitat suitable for passerines has increased. 6 R1 _# y) x# e. [% p" Y/ ^- m3 D
答案A |