丙烯在空气中的爆炸极限是（）
参考答案：2.0~11.1%
It is the first time I _____ visitors since I moved to London.[ ]
A. had had
B. have had
C. have
D. had
患者，男性，62岁，胃大部切除术后行空肠造瘘。该患者饮食应采取
A．低脂肪饮食B．半流饮食C．流质饮食D．少渣饮食E．要素饮食
