74. Must ， have to者都表示“必须”

74. Must ， have to者都表示“必须”，
must侧重于说话者的主观看法， 它不随人称或时态的变化而变化。
As students ，we must work hard.
Betty said she must go shopping with me.

have to则侧重指客观需要，含有“不得不”或“被迫”之意。而且有人称和时态的变化。
It's raining heavily. They have to stay at home and watch TV.
The boy's father died when he was 12 years old. So he had to leave school and work.