She exhibited great powers of endurance during the climb().

单项选择题People did not begin to use unmanned vehicles in undersea exploration until recently because of().

A. the communication problem
B. the ocean depths
C. the movement of waves
D. the problem of vacuum

单项选择题51（）

A.built
B.designed
C.intended
D.lined

单项选择题Cutting trees to grow more food may hamper a developing country in its fight against poverty.()

A. Right
B. Wrong
C. Not mentioned

单项选择题By more challenging (Para. 6), the author means ().

A. more interesting
B. more demanding
C. more attractive
D. more’dangerous

单项选择题Among humanity’s current problems, the chief concern of the scientists is the reduction of biological diversity.()

A. Right
B. Wrong
C. Not mentioned