复面洞制备时,对髓壁的要求是()
A.侧壁垂直
B.与龈壁垂直
C.与轴壁平行
D.侧壁平行
E.以上都不对
参考答案:A
They are always singing songs to ________ their spirits when they meet with trouble.[ ]
A. keep off
B. keep back
C. keep up
D. keep on
环毛蚓自XⅠ/XⅡ节间沟开始,于背线处有(),可排除体腔液,湿润体表,有利蚯蚓的呼吸作用进行和在土壤中穿行。