21£®The experiment turned out to be______ failure, but as we know, Success often comes after_____ failure.

A£®a£»a                    B£®/£»/                        C£®a£»/                  D£®/£»a

22£®_____trying to persuade his father to give up smoking, his letter was rejected.

A£®Aiming at           B£®Aimed at                 C£®Being aimed at    D£®to aim at