小儿急性喉炎的临床表现可有()。
A.声嘶
B.犬吠样咳嗽
C.吸气性呼吸困难和喉喘鸣
D.三凹征阳性
E.发热、烦躁不安、无力、紫绀等
参考答案:A, B, C, D, E
(2013·威海两校模拟)________ the earth to be flat, many feared that Columbus would fall off the edge of the earth.
A.Having believed
B.Believing
C.Believed
D.To believe
当k=______时,关于x,y的多项式-x2+2kxy-4y2+xy-5x+1中不含有xy项.