The train ________ at 7∶00, we have been waiting for as long as two hours．

A．must have arrived

B．might have arrived

C．was supposed to arrive

D．should arrive

He is supposed ________ abroad, but no one knows which country he was in．

A．to be studying

B．to study

C．having studied

D．to have studied

We ________ the prosperity of our country．

A．are proud

B．are pride of

C．take pride in

D．take proud in

The boy got full marks in math so he was very ________ of himself．

A．pleased

B．angry

C．proud

D．disappointed

He ________ home once a week, but after entering middle school, he ________ home once a month．

A．was used to go;was used to go

B．used to go;was used to go

C．was used to go;used to

D．used to go;was used to going

We must ________ what caused the accident．

A．find

B．find out

C．discover

D．invent

It is well known that Thomas Edison ________ the electric lamp．

A．invented

B．discovered

C．found

D．developed

________ catch the train, he took a taxi to the railway station yesterday．

A．In order to

B．So as to

C．In order that

D．So that

The young child ________ and fell onto the ground．

A．lost his balance

B．take the balance of

C．on balance

D．upset the balance

Usually, gold scarcely ________ in water, which is one reason why it is such a precious metal．

A．melts

B．dismisses

C．dissolves

D．resolves