中子或质子束可引起()
A.雪盲
B.日光性视网膜病变
C.放射性视神经病变
D.吹玻璃工人白内障
E.视网膜出血
参考答案:C
已知a既不是正数,也不是负数,则-a+1=______.
I must leave now. I have to ______ goodbye to you. [ ]
A. talk
B. tell
C. say
D. speak