第一类, 感觉动词, 所接的宾补可以是v-ing形式,也可以是动词原形。 feel, hear, listen to, notice, observe, see, watch, look at
1. I saw him ____________ (cross) the road. 2. He was seen _______________ (cross) the road.
cross/crossing
to cross/ crossing
但变为被动语态时,不定式要带to