Then we expound the gross designing course and main contents of PBL Web-based course based on PBL and instructional design centered on learning activity.
然后在以学习活动为中心的教学设计理论和PBL 的基础上，提出PBL网络课程的总体设计过程和主要设计内容。
Roots developing and activity: The amount of white roots and yellow roots and the average gross roots are more in the pressed area compared to the traditional area.
碾压处理区白根、黄根数量多，平均总根量大于对照区，说明碾压后土壤具有较好的保水保肥能力，有利于根系生长发育；
Roots developing and activity: The amount of white roots and yellow roots and the average gross roots are more in the pressed area compared to the traditional area.
碾压处理区白根、黄根数量多，平均总根量大于对照区，说明碾压后土壤具有较好的保水保肥能力，有利于根系生长发育；
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