Tommy had his big brother _____ his shoes for him.

A．to tie

B．tie

C．tied

D．tying

关于咯血与呕血的鉴别，下列错误的是（）。

A.咯血不可能出现黑便，呕血一定出现黑便

B.咯血为鲜红色，呕血多为暗红色

C.呕血见于消化道疾病

D.咯血属碱性，呕血属酸性

E.咯血中混有痰、泡沫，呕血混有食物残渣、胃液