BTn.BT菌（一种致命细菌）abbr.比特流；一种内容分发博议（=Bit Torrent)abbr.准男爵（=baronet）abbr.神学士（=Bachelor of Theology）BTTn.银行出纳员终端

1. The clock began to whirr before striking the hour.
   钟在打点前先嘎啦嘎啦地响起来。
2. The spark is therefore timed to occur before the piston reaches top dead center, otherwise maximum pressure would not be reached in time.
   因而，在活塞到达上死点前，火花便会发生，否则就不可能适时达到最高的压力。