哪种实验动物是营养学、生理学、药理学、毒理学、行为学及外科手术学等方面实验研究常被选用的实验动物（）。
A.小鼠
B.豚鼠
C.家兔
D.犬
参考答案：D
—Where is your uncle?
—He _____ to South Africa on business. He has ______ there twice.
A．has been; gone
B．has gone; been
C．went; gone
D．will go; been
