Our school forbids ________, that is to say, we are not allowed ________ at school.[ ]

A. to smoke; to smoke  

B. smoking; smoking

C. to smoke; smoking  

D. smoking; to smoke

一个圆柱形玻璃容器内盛有水，把一段横截面半径是5厘米的圆钢全部放入水里，水面上升9厘米；再让水中的圆钢露出8厘米长，这时容器内的水就下降4厘米，这段圆钢的体积是多少？