亚声速流动，是指马赫数（）时的流动。
A.等于1
B.等于临界马赫数
C.大于1
D.小于1
参考答案：D
This book is very interesting, and it is worth ________ again.[ ]
A. to read
B. reads
C. read
D. reading
患者小腿部红肿瘙痒，外治应首选
A．金黄膏B．青黛膏C．红油膏D．白玉膏E．冲和膏
