【C12】A．onceB．beforeC．becauseD．and

A．Because scientists like mosquitoes.B．Because mosquitoes adapt quickly and can change

A．Because there was a shortage of men and women in the area.B．Because mining communiti

A．Because their environment is becoming more and more dirty.B．Because the traditional

【C12】A．by or largeB．by and againC．by and largeD．by and by

【C12】A．all at onceB．once moreC．by and largeD．by and by

【C12】A．theB．aC．anD．／