Question

An old lady was crossing the street in front of my car and I ________ stop very quickly.

1. A.
   must
2. B.
   have to
3. C.
   has to
4. D.
   had to

Answer 1

D
剖析：must表示说话人的主观看法，意为“必须、应当”；而have to则表示客观需要做的事情，第三人称单数形式用has to，过去式用had to，意为“必须，不得不”．