单选题：Researchers sometimes become__________when their efforts app

题目内容：

Researchers sometimes become__________when their efforts appear to produce less obvious results. A．encouraged
B．relieved
C．frustrated
D．disgusted

参考答案：

答案解析：

阅读以下材料，回答题：The author's attitude towards the current situati

阅读以下材料，回答题：The author's attitude towards the current situation in the exploitati

分类：英语题型：单选题

The people who objected to the new airport were told that since the work had　alr

分类：英语题型：单选题

从事生产、经营的纳税人，应当自领取营业执照之日起（　）内，向生产、经营地或者纳税义务发生地的主管税务机关申报办理税务登记。

分类：英语题型：单选题

分类：英语题型：单选题

分类：英语题型：单选题