甘氨酸和丙氨酸最多能形成二肽（）
A.1种
B.2种
C.4种
D.6种
参考答案：B
Miss Liu, can you speak aloud? I can______ hear you.[ ]
A. clearly
B. slowly
C. badly
D. hardly
The old man is ________ enough to contribute $ 10,000 to the disaster area damaged by the earthquake.
A．considerate
B．generous
C．fashionable
D．concerned
