21. John was so sleepy that he could hardly keep his eyes__________
.
A. open B. to be
opened C. to open D. opening
22 _________ a reply, he decided to write again.
A. Not receiving B.
Receiving not C. Not
having received D. Having not
received
23Charles
Babbage is generally considered ______the first computer.
A. to have
invented B. inventing C.
to invent D.
having invented
24___ down the
radio-the baby's asleep in the next room.
A. Turning B.
Turn C.
Turned D.
To turn