21．There is a saying，yesterday is history, tomorrow is a mystery．But today is_______ gift．That is why it's called _______ present．
A．＼；＼ B．the；a C．＼；a D．a；the
22．Text messages can be a good way to spread information，particularly to groups who are hard to reach by _______ means，such as teenagers．
A．another B．other C．the other D．others
