21、根據(jù)下面內(nèi)容，回答21-35題：
Scientists in the UK have announced that the piranhafish's reputation 21 a fearsome 22 may well not be deserved. The fish, which is found in the Amazon in Brazil, have been 23 as deadly carnivores( 食肉動物 ) that work in shoals to overwhelm their prey and strip it of its flesh in seconds.
However, experts 24 St Andrews University say that piranhas are omnivores(雜食動物) that mainly eat fish, plants and insects. They form big groups not to hunt but to defend 25 against other predators, according to the team.
"Previously it was thought piranhas shoaled as it 26 them to form a cooperative hunting group," said Professor Anne Magurran. " 27, we have found that it is primarily a defensive behavior. "
Piranhas can be attacked by animals 28 dolphins, caimans and large fish, so forming a shoal is a good way of 29 being killed. Piranhas of 30 age stay in the middle of the group for 31 and the 32 of the shoal differs according to the level of 33 When the water level is 34, the fish form small groups as there is space to escape, but when the water level drops, they form large groups as protection 35 predators.
A．a(chǎn)s
B．a(chǎn)s if
C．a(chǎn)s though
D．since
22、
A．kill
B．killer
C．murderer
D．murder
23、
A．told
B．saying
C．describing
D．portrayed
24、
A．out
B．with
C．from
D．by
25、
A．them
B．themselves
C．it
D．itself
26、
A．a(chǎn)ble
B．is able
C．enable
D．enabled
27、
A．Thus
B．However
C．Suddenly
D．Therefore
28、
A．such
B．example
C．like
D．a(chǎn)s such
29、
A．prevent
B．preventing
C．a(chǎn)void
D．a(chǎn)voiding
30、
A．reproduce
B．reproductive
C．reproduction
D．reproductively
31、
A．protection
B．protecting
C．protect
D．protective
32、
A．rate
B．size
C．a(chǎn)mount
D．percentage
33、
A．fate
B．destiny
C．risk
D．chance
34、
A．high
B．low
C．peaceful
D．chaotic
35、
A．for
B．a(chǎn)gainst
C．without
D．towards
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