(2009年合肥市高三第一次教学质量检测)The police tried to get some clues from the suspect，but he remained     ．

We used to see each other       , but I haven’t head from him since last year.

Deserts, dry areas with _____ no vegetation, cover more than one-third of the Earth's land surface.

With the word“PM2．5"_____ appearing in media reports，people pay greater attention to it and seek health tips for smoggy days．

—Where have you been? —I got caught in the traffic jam; ______ I’m here just on time.