Tom took a taxi to the airport, only _____ his plane high up in the sky. [ ]

A. finding          

B. to find          

C. being found      

D. to have found

立克次体与病毒的不同特点是

A．有两种核酸
B．人工培养基中不能生长
C．以节肢动物为传播媒介
D．仅引起局限于某一脏器的感染
E．致细胞裂解