填入介词或副词

to
of
at
at
against/on
with
for

1.He makes several business visits_to__America every year
2.We rode through a herd__of_cows
3.I have_at__most 200 foreign stamps
4.The round-trip tour begins_at__the cave's historic entrance
in Hell Canyon
5.Hebanged his head _against_the wall
6ibecame dizzy _with__all the do's and the don'ts,and how'sand
the why's
7.We have asked the Conrads to come__to__dinner on Friday
evening