21．It is likely that water is not ____ endless resource, nor ____ that can be made once more．
A．the; / B．an; one C．an; that D．/; one
22．According to a UN report, one third of the world population have no ____ to clean drinking water and health care．
A．means B．approach C．channel D．access
23．--- You won’t go to Mary’s wedding, will you?
--- No, _____ invited．
A．if B．once C．though D．in case
24．--- Mum, I don’t want to take the medicine．
--- Oh dear, you should know that good medicine for health ____ to the mouth．
A．tastes bitter B．tastes bitterly C．is tasted bitter D．is tasted bitterly
