方法一:自交
操作:____;
实验结果及结论:____.
方法二:杂交
设NA为阿伏伽德罗常数的值.下列说法正确的是( )
勿以善小而不为,____。
下列关于力的说法,错误的是( )
—Mum, I have a bad headache. I feel terrible.
—Oh, dear! You must get a cold. You'd better see ___________ after breakfast.