三系即不育系，保持系，恢复系。三系法主要是用于配套不育系育种。
油菜杂种优势利用途径主要有三系法和两系法。
父本R40 2是湖南安江农校选育成的三系法早杂恢复系。
Its paternal parent"R402" is a three-line hybrid restorer line of early rice.
你还应在教育系学两门三个学分的课程。我建议你学教育心理学和视听法及视听设备。
You also should take two three-credit courses in the Education Dept. I suggest Educational Psychology and Audio-visual Methods and Aids.
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