In "Standing at the door, I saw some girls chatting at a table", the italicized part is us

I （)supper when I（)someone knocking at the door.A、made . . . HeardB、made . . .was heard

The salesman approached the house cautiously when he saw the vicious dog at the door.A.c

At the bank the day before yesterday, I was standing in a line______around some loose velv

I almost jumped out of my skin when I saw my boyfriend at the movie theater with another g

I _________ （watch) TV when someone knocked at the door．

Mary _______ be at home. I saw her in the library