下图所示双代号网络计划的关键路线为（）。
A．①-⑧
B．①-②-⑥-⑧
C．①-③-⑦-⑧
D．①-④-⑤-⑦-⑧
参考答案：D
The boy was able to __________ himself when he was very young.
A．dress
B．wear
C．put on
D．wears
如何防止农膜对土壤的污染？
