题目内容：
Every few years, the coal workers ______ their lungs X-rayed to ensure their health.
A. are having
B. have
C. have had
D. had had
参考答案：
选择题：Every few years, the coal workers ______their lungs X－rayed to ensure their heal
- 题目分类：习题答案
- 题目类型：选择题
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