They can surely overcome those difficulties they are closely united.A. even ifB. as long

问题补充：

They can surely overcome those difficulties they are closely united.

A. even if

B. as long as

C. so long as

D. B and C

答案：

A. even if

B. as long as

C. so long as

(答案→)D. B and C

解析：as long as，so long as（只要），是引导状语从句的连词，表示条件。