It ________ some time _________ I realized the truth.
A．was; before B．is; before
C．has been; until D．has been; after
The annual Energy & Environment Conference calls on our human beings to _______environmental issues.
A．care for B．care of C．care about D．care in
--- We need someone to host the New Year Party.
--- ________ the handsome young man have a go?
A．Need B．Must C．Shall D．Will
Being a teacher always encouraging students to think for themselves, I won't tell them answers until they __________ on a math problem for more than an hour.
A．have worked B．will have worked
C．will have been working D．had worked
He could speak English fluently because he __________ it for four years when he was a college student.
A．had studied B．have been studying C．studied D．was studying
Looking at my mother's ___________ face, I regretted not having told her my whereabouts on the phone.
A．worrying B．worried C．anxioused D．satisfied
