Question

语法填空

Koalas, native to the Australian wilds, initially proved difficult to keep alive in zoos, because koalas eat nothing but the leaves of the eucalyptus tree(桉树). Zoos provided them ____1.______ an unlimited supply of eucalyptus leaves. One zoo even planted eucalyptus trees _____2.____(make) sure that the koalas had a continual supply of fresh leaves. However, koalas kept in cages always died within a year of their ___3._____(arrive) at the zoo.

Eventually it was discovered that eucalyptus trees less than five years old sometimes produce a kind of acid in their leaves. Taking in small quantities of this acid ___4.____ (be) fatal to the koalas. In their natural habitat, the koalas’ senses tell them ____5.____ eucalyptus trees have dangerous leaves, and they simply move on to other trees until they find leaves _____6.____ are safe to eat. But in zoos, when their keepers unknowingly were giving them leaves with acid, the koalas ____7.____(leave) with only two options: eat the poisonous leaves ____8.___ starve. Either option was fatal to the ____9._____(trap) koalas.

Fortunately, today’s zoos use special tests to distinguish between poisonous eucalyptus leaves and safe ___10.______, and now koalas are eating well and living an easy life in zoos.

Answer 1