______ of the twins passed the exam because they worked hard at their lessons.

单项选择题How happy we are ______ each other here away from home!

单项选择题______ the window. What's happening there

单项选择题______ bad weather we are having! We've never had ______ rainy days.

单项选择题He is so fat that the chair is not large enough for him to ______.

单项选择题有机体对条件刺激和条件刺激相类似的刺激作出一样的反应，巴甫洛夫称之为( )。