While we were running on the playground, Jack suddenly stopped ________ and lay on the ground,

so we all stopped ________ what was wrong with him. [ ]

A. to run; to see

B. running; seeing

C. running; to see

在冬季可以往齿轮油中掺兑煤油或柴油，以降低凝点，从而保证正常润滑