______, the professor is still trying to learn a new language.

A．educational

B．political

C．commercial

D．social

A．The honey-bee is blind to red.

B．Man is more color-conscious than the honey-bee.

C．The honey-bee can see far more colors than man.

D．Man is sensitive to the ultraviolet.

A．which

B．where

C．that

D．when

A．gives up

B．eats up

C．takes up

D．breaks up

A．in

B．off

C．out

D．on

A．to write about

B．to write with

C．to write

D．to write in

A．At times

B．At a time

C．At all times

D．At no time

A．Possibilities

B．Chances

C．Possible

D．Probabilities

A．like

B．possible

C．likely

D．probable

A．on schedule

B．on purpose

C．at random

D．at large