The scientists are trying out the new medicine to see how well it works。()

A.weren't; were

B.aren't, were

C.weren't; are

D.aren't; are

A.if

B.whether

C.that

D.as

A.A.Once

B.B.Since

C.C.Though

D.D.Unless

Scientists are certain that the sea level____rise in the next 200 years.

A. is going to

B. may

C. will

D. should

Scientists resist talking about their options because they don't want people to

A know what they are doing.

B feel their efforts are useless.

C think the problem has been solved.

D see the real problem.

The reasons why birds don't get lost on long flights______.

A．have been known to scientists for years

B．have only recently been discovered

C．are known by everyone

D．will probably remain a mystery

With the population explosion, scientists will have to() new methods of increasing the worlds food supply.

A.lead to

B.carry out

C.come up with

D.stick to

A.with

B.on

C.to

A.didn't achieve

B.wasn't able to achieve

C.wouldn't have achieved

D.shouldn't have achieved

A．have been known to scientists for years

B．have only recently been discovered

C．are known by everyone

D．will probably remain a mystery

A、before long

B、until recently

C、long before

D、in the past few years