The pumps press oil into the cross－head bearing gap when the load on the shell is at its l

The pumps press oil into the cross-head bearing gap when the load on the shell is at its lowestWhat is the meaning of “its” in the sentence above？

A.the cross-head

B.the pumps

C.the shell

D.the load

请帮忙给出正确答案和分析，谢谢！