-Have you heard of Earth Day? Yes We have only one Earth. We have no choice but i

问题补充：

---Have you heard of Earth Day?

--- Yes, We have only one Earth. We have no choice but it.

A. protect

B. protected

C. protecting

D. to protect

答案：

A. protect

B. protected

C. protecting

(答案→)D. to protect

解析：

试题分析: 句意：你听过地球日吗？听过，我们只有一个地球，我们除了保护它别无选择。Have后接带to不定式，故选D。