Bob and I ___ good friends.
--- ______ do you improve your listening skills? --- I improve it _______ listening to tapes.
_____the old lady is seventy years old ,_____is still lively.
___students will take part in the sports meeting and _____them is over three hundred.
—Can you play volleyball? —Yes, ________.
My Chinese teacher told me that it was ___known that China is a big country.