有这样两个选择题.1、While watching television,--------.A.the doorbell

有这样两个选择题.1、While watching television,________.A.the doorbell rangB.the doorbell ringsC.we heard the doorbell ringD.we heard the doorbell rings我选的是D,但答案是C.为什么?2、——Did Jack come back early last night?——Yes.It was not yet eight o'colck_______ he arrived home.A.before B.when C.that D.until我选的是D,为什么?我明明记得有个句式是“it was not ...until.”的?