The ratio of the work done by the machine（）the work done on it is called the efficiency of the machine.

单项选择题His inability to learn foreign languages was a(n（）to his career.

A.objection
B.defect
C.obstacle
D.depression

单项选择题In general , the amount that a student spends for housing should be held to one-fifth the total（）for living expenses.

A.acceptable
B.available
C.advisable
D.applicable

单项选择题When you go to the doctor he asks you to describe your（）so that he can make a diagnosis (诊断).

A.indications
B.signs
C.symbols
D.symptoms

单项选择题He ran so fast that he was out of（）

A.air
B.oxygen
C.breath
D.wind

单项选择题Be careful with those fireworks; they are（）to go off unexpectedly.

A.easy
B.probable
C.available
D.liable

单项选择题Most people who travel in the course of their work are given travelling（）

A.income
B.allowances
C.pay
D.wages

单项选择题The suspect's fingerprints on the gun were the main（）against him.

A.crime
B.information
C.conviction
D.evidence

单项选择题Humidity (湿度) is so intense in some parts of the tropics that Europeans find they are unable to（）it.

A.maintain
B.persist
C.endure
D.sustain

单项选择题The republication of the poet's most recent works will certainly（）his national reputation.

A.magnify
B.enlarge
C.strengthen
D.enhance

单项选择题Having come from a（）society, Dick found it hard to adjust to a small town.

A.abundant
B.wealthy
C.sufficient
D.large