下突变中哪个很少有可能产生回复突复：（）
A.点突变
B.颠换
C.转换
D.染色体上三个碱基的缺失
参考答案：D
Sara felt very ____when everyone laughed at her question.[ ]
A. boring
B. disappointed
C. embarrassed
D. encouraged
----Is Peter there?
------ _______, please. I’ll see if I can find him for you.
A．Hold up
B．Hold on
C．Hold out
D． Hold off
