题目

John put his wallet into the microwave oven _________.   A. for keeping safe                    B. for the safety   C. to be safe keeping                      D. to keep it safe 答案：D学校运来一堆河沙准备填沙坑。沙堆是圆锥形的，量得沙堆的底面周长是6.28米，高是2米，已知每立方米的河沙大约重1.5吨。这堆河沙重（__________） 吨.