婴幼儿易患呼吸道感染的免疫因素是呼吸道黏膜缺少()
A.SIgA
B.IgM
C.IgG
D.IgE
E.IgD
参考答案:A
My cousin Andy can play _______ piano very well, buy he isn't good at playing ______ basketball.
A.the; the
B./; the
C.the; /
D./; /
解释商务礼仪的作用。