问题
选择题
---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
答案：D
题目分析: 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。