( ) Even the top students in our class can’t work out this problem. So it _____ be very difficult.
| A．may | B．must | C．can | D．need |
( ) Chinese people invented paper for 
.
| A．we | B．us | C．our | D．I |
( ) Nine children
their grandparents last week.
| A．visits | B．visit | C．visiting | D．visited |
( ) The man sits
under the tree.
| A．at | B．up | C．down | D．in |
( ) The mouse is 
front of the cat.
| A．on | B．in | C．at | D．to |
( ) 
first, I fell over. But it didn’t hurt.
| A．On | B．In | C．At | D．To |