In the past three summers, increasing numbers of migratory marine mammals
- p! I7 ^/ T" i3 _" p* F/ `" } have died in the Gordon City Bay area. It is now hypothesized that certain clean -' I3 h. J1 E, _
ing products for ships' hulls which contain the chemical LSA are responsible for * t$ ^* J9 ]. R" Q( k n! v
the deaths. LSA, which weakens mammals' defenses against infections, has 8 o$ X' S: u, L, N
been found in tissue samples from many of the dead animals and, significantly, 5 M, d4 h$ E9 Y/ m- _$ {* W
the animals died of a viral infection not usually fatal to them.& r X( f+ H) i
Which of the following, if true, most strongly supports the hypothesis given?
+ C% Y! P$ k/ } A The cleaning products containing LSA came onto the market about four + s! v. |6 s: l* l3 }& L
years ago and have, because of their superior effectiveness in cleaning 4 C1 {; F( I" x' k: [# @, P
ships' hulls, displaced the cleaners previously used.
. ]5 `" F! H0 X( p2 M& f B Tissue samples from the dead marine mammals have also been found to
; @! ]2 j: W) y0 w contain many substances other than LSA that are toxic to marine mammals.
* L% d& L/ D' _8 C+ S _5 J C There are some indications that the virus that caused the deaths of marine
; o. @$ ^; o3 M/ W mammals around Gordon City Bay has mutated in recent years into a more
2 x4 W+ J; ^. Q g/ ` harmful form. 1 X9 l$ V( T9 ? j; B& Q1 e% ~
D Few of the marine mammals summering around Gordon City Bay ever stray
- x1 y3 `. y. K5 Y into Gordon City harbor and its extensive seaport facilities.
: s6 _3 W# \" a, t* x E During the past three years in Gordon City Bay, there have been a number
* g; `1 X/ q% b& w of fairly large fish kills in addition to increased deaths of marine mammals.
G, d/ Z) y" d答案：A |
发表于 2012-8-15 12:40:43
