做豌豆杂交实验的遗传学家是（ ）
A．虎克
B．达尔文
C．孟德尔
D．施莱登
答案：C
____ Christmas Eve, children put a stocking ____ the end of their beds before they go to sleep.[ ]
A. On; at
B. In; at
C. At; on
D. In; on
什么是测量误差？
