2009年4月24日，美国宇航局为了纪念庆祝地球日，特意发布了具有代表性的一组地球图片。这些照片是过去50年来从太空角度观测地球最令人惊叹的图片，从图片上看，地球大部分是蓝色的，这是因为（   ）

根据句意，用括号内所给动词的适当形式填空。(必要时加助动词或情态动词)
____ Mr Zhang ______(teach)us English three years ago.
____ Peter turned off the computer after he finished______ (write)an e-mail.
____ —Where's Miss Wang?一Look，she______(talk)with the students.
____ Mr Liu isn't here now．He______ (go)to Beijing.
____ The children will go to the zoo if it______ (not rain)this Saturday.
____ There______ (be) a meeting in our school tomorrow afternoon.
____ Mr Green______(watch)TV at this time last night.
____ You’d better______(eat)less food before you go to bed.
____ My teacher told me that light______(travel)much faster than sound.
____ English______ (speak) by many people in the world.