. Although the population of a certain salmon species in the Pleasant River 4 s# Z& s* p0 p# E8 W
has not decreased in the last five years, the average size of adult female ( w. c1 S1 b- K7 X2 I7 N0 B- x
salmon of that species in the river has decreased significantly in this time. `; a- @% {1 m. F" ?, n5 q3 n( N
The latter fact indicates that the population of this species is ultimately 7 B( T$ X% b! T, Z
endangered, since small fish of a given species lay far fewer eggs than
, Q+ d: u; O! k% {+ @do large fish of the same species.. i5 ^( `" ]; V. O7 v
Which of the following is an assumption on which the argument depends?
. l) X3 l& B/ i- | A Excluding fish of the salmon species, the average size of fish in the
_& R9 i$ }9 m' y) H Pleasant River has increased over the past five years. . @6 T/ h" A; k# P! w6 p9 o
B The largest adult female salmon living in the Pleasant River five
6 a/ u3 ~' N+ Q+ `. V years ago were significantly larger than the largest adult female
6 \! i4 I9 q$ N" s* p salmon living there now. , k s/ a& u; K0 w
C Smaller salmon are not an easier prey for salmon predators than are
3 J6 b9 p& s: B larger salmon.
3 n m9 Z' g) `* u8 Z D The total number of eggs laid each year by salmon of the species " r& X- S) i& S5 f# m7 A$ g. A
in the Pleasant River has not varied significantly over the past five : D. D7 c* C1 X' F. e
years.
% g" B' N, U. e: P+ O7 h( m. s0 \9 h) O E The proportion of the eggs laid by small salmon of the species that * P4 D6 ^# y9 K2 @( Q6 U5 x
hatch into fish that reach reproductive maturity is not significantly / H4 Y# _- z: ~5 ?: Z8 _
greater than that of the eggs laid by large salmon of the species. 5 ?" E3 [* @- X4 _8 x5 v- v3 \
答案E |