半助动词 be bound to
问题描述：
半助动词 be bound to
He must be in the office.=He is bound to be in the office .为什么?能用be sure to
答
be bound to 表示注定要、计划好的意思
must 表示一定要、迫于压力的原因
两者意思差不多.
be sure to = be bound to 一定要... 所以可以替换.