You must be very tired 改成宾语从句前面是Lin Tao said Jim具体的Lin Tao告诉Jim：你一定很累lin Tao：You must be very tired

Lin Tao said Jim must be very tired

Lin Tao said/told Jim that he must be very tired.
一般情况下，用that引导宾语从句；注意在从句中主语人称的转换（you转为he）

Lin Tao said to Jim whom must be very tired.

Lin Tao said to Jim that he must be very tired.

Lin Tao told Jim that he must be very tired.

Lin Tao said Jim was tired.

Lin Tao said that Jim must have been very tired.
从句要用情态动词加现在完成时的形式表示过去～

Lin Tao said Jim must be very tired.

Lin Tao said that jim must be very tired.