若等腰三角形腰上的高是腰长的一半，则这个等腰三角形的底角是[ ]

A.75°或30°

B.75°

C.15°

D.75°或15°

根据下列句子所给汉语意思或提示，写出空缺处单词的正确形式。

小题1:Scientists are ________ (调查) into the cause of cancer.

小题2:To get the job done, one should be ________(精力充沛) and hard­working.

小题3:As a ______（奖赏）for passing her exams, she got a new bike from her parents.

小题4:Dilma Rousseff, who won 56% of the _______ (选票), was elected President of Brazil.

小题5:The old lady likes          (spy) into other people’s affairs.