哮喘的典型症状是
A.反复发作的吸气性呼吸困难B.反复发作的呼气性呼吸困难C.反复发作的混合性呼吸困难D.逐渐加重的咳嗽、咳痰、呼吸困难E.一过性的混合性呼吸困难
参考答案:B
Which of the following statements is NOT true of the passage
A.It discusses fertility clinics.
B.It defines stem cells.
C.It mentions artificial fertilization.
D.It identifies the origins of stem cells.
“一手交钱,一手交货”是物流与商流统一的交易形式。( )