—I don't know how to pronounce this word. Can you help me?

—Sorry, I don't know, either. Let's _____ in my dictionary right now. [ ]

A. look it up

B. look up it

C. look them up

D. look up them

1岁以内小儿心力衰竭最常见的原因是

A．先天性心脏病

B．心律失常

C．心肌炎

D．心内膜弹力纤维增生症

E．缺血性心脏病