A:What
B:Why
C:It
D:That
由天然放射性元素钋(Po)放出的α射线轰击铍(Be)时会产生A粒子流,用粒子流A轰击石蜡时,会打出粒子流B.下述正确的是( )
Our school is so famous that _______ people come and visit it every term.
读甲、乙两图,有关叙述正确的是( )