以下关于表皮组织结构特点描述正确的是()
A.表皮组织来源于中胚叶
B.表皮属复层扁平上皮
C.基底细胞能产生黑色素,保护免受光线损伤
D.表皮有丰富的血管网
参考答案:B
If it had not been for your help, I ____ the examination.
A.could not pass
B.would not pass
C.would not have passed
D.can not have passed
包装机设备运行环境温度应为()
A.0到20摄氏度
B.0到30摄氏度
C.0到40摄氏度
D.0到50摄氏度