从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
21．Though ________ failure is the mother of success，everyone wishes to have ________ success.
A．/；a B．the；a C．a；a D．/；/
22．Every day before going to school，we are________to be careful when crossing the street.
A．kept B．demanded C．required D．hoped
23．She was angry with me，but she didn’t shout，just________me silently.
A．glancing at B．watching at C．looking at D．glaring at
24．Scientists ________ that global warming would make the icebergs in the Arctic melt in five hundred years.
A．inform B．predict C．promise D．trust
25．The parents sat still with________their daughter，who was dancing beautifully on the stage.
A．their eyes fixed on B．their eyes fixing on
C．their eyes fixed to D．their eyes fixing to
26．Little Tom________finished his homework；otherwise，he wouldn’t be listening to music.
A．can have B．must have C．should have D．might have
27．You’d better stop playing Internet games. There is evidence of a(n) ________ between headaches and computer use.
A．combination B．connection C．organization D．association
28．The president refused to________the rumor that he had murdered(谋杀) the former president.
A．confirm B．admit C．accept D．realize
29．________to his research，my father spared no time to spend a weekend with us.
A．Devoting B．Devoted C．Caught D．Lost
30．At the news of the accident，the girl can’t help ________ worried.
A．get B．to get C．getting D．but getting
