What actually ______ the accident has not yetbeen determined

in 2011, the Beijing-Shanghai high-speed railway has benefited Qufu a lot.

Many volunteers______ food and water to the local people in Japan after thetsunami.

nager was worried about the press conference his assistant ______ in his place but, luckily, everything was going on smoothly.

wasold,MrSmith_____sitforhourswithoutsayinganything.