题目选项分析

Reporting that one of its more crippling malfunctions is the sudden and unexpected failure of the liquid helium cooling system, the engineering squad supervising the Large Hadron Collider requested additional funding to develop better maintenance systems.

Reporting that one of its more crippling malfunctions had been the sudden and unexpected failure of the liquid helium cooling system, the engineering squad supervising the Large Hadron Collider requested additional funding to develop better maintenance systems.