21．“Have you seen _______ new bike? I put it here just now．”
“Is it _______ white one? A boy has ridden it away．”
A．a, the B．the, the C．a, a D．the, a
22．Many scientists have believed that there may be a _________of life on the Mar．
A．mark B．signal C．sigh D．sign
23．When the peace talk failed．There was a fear that war may ____________ at anytime．
A．break off B．break up C．break out D．break down
