土壤耕性
参考答案：土壤耕性指土壤容易耕作的程度。土壤耕性的好坏以耕作的难易程度，耕作质量好坏，宜耕期长短来衡量。
Was it _____ he was playing volleyball on the playground _____ he got hurt?
A．that; when
B．when; that
C．that; where
D．where; that
锅炉按循环方式可分为自然循环锅炉、多次强制循环锅筒锅炉、低倍率循环锅炉和直流锅炉。( )
