根据句子意思,用括号中所给词的正确形式填空,每空填一词。
Seven ____ (twelve) of the students have taken part in the tree-planting activity since Monday.
设向量a→,b→不平行,向量a→+λb→与3a→+2b→平行,则实数λ=____
进入血液的氧,通过血液循环输送到全身各处的组织细胞内的什么部位被利用?( )