环境问题已成为制约社会发展和进步的严重问题.有下列几种说法,正确的是____ .
①臭氧层的主要作用是吸收紫外线②温室效应将导致全球气候变暖 ③酸雨主要是由于空气受到硫的氧化物和氮的氧化物污染所致 ④光化学烟雾主要是由汽车排放的尾气引起的
我国人口分布的特点是( )
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.