They repeatedly recommended that our social security system（ ）co

They repeatedly recommended that our social security system（ ）cover many of the occupants.
A、being extended
B、extended to
C、had extended to
D、be extended to
【正确答案】：D
【题目解析】：当主句里含有表示意志的成分时，后面的that分句中谓语动词通常使用原形。例如主句中含有advise，insist，recommend，suggest等