A. thoughB. as C. while D. for [解析]B､C｡作并列连词时,when/while用法较为特殊,二者区别是:while表两相对照;而when表突然､在那时,常见于be about to do...when和hardly...when等句型中｡ 考点二、表示原因的连词for/because/as/since ...
?Unfortunately, as the number of people living in the city increases, so do the different problems associated with population growth. (注意此句中的so不表示“所以”,而是“…也…”的意思) 3. thanks to(positive situations通常适用于结果好的时候) ...
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