Find ways to praise your children often，________ you’ll find they will open their hearts to you.

A．till

B．or

C．and

D．but

在矿烧目前的条件下，烧结终点应控制在倒数第二个风箱，为确保冷却效果不出红块，烧结终点不许后移超过倒数第二个风箱。