Every few years, the coal workers                 their lungs X-rayed to ensure their health.

1. A.
   are having
2. B.
   have
3. C.
   have had
4. D.
   had had

Every few years, the coal workers         their lungs X-rayed to ensure their health.

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

Every few years, the coal workers ___________ their lungs X-rayed to ensure their health.

 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