题目

____ do you study for tests?  I work with my friends.      A. How   B. Who   C. When 答案：A用α粒子轰击某原子核Z，产生一个C和一个中子。由此可知A．x=8，y＝3     B．x=9，y＝5C．x=8，y＝5 w_wD．x=9，y＝4