当直线平行于投影面时，直线在该投影面的投影具有（）性。
A、收缩
B、积聚
C、真实
参考答案：C
铅对γ射线屏敝较好。
If he can __________ his ability with hard work, he should be very successful.[ ]
A. realize
B. develop
C. combine
D. train
