原发性肠套叠有以下特点()
A.随着年龄增长发病率降低
B.有明显病因
C.常见于2岁以下婴儿
D.套叠段无明显的器质性因素
E.男孩是女孩的2~3倍
参考答案:A, C, D, E
John had to have his car repaired in a garage because it seriously.
A.damaged
B.was being damaged
C.had damaged
D.had been damaged
为确保废水放总量监测数据的可靠性,应如何做好现场采样的质量保证?