【简答题】用括号里所给单词准确形式填空 Rafting is an___1__ (excite) adventure. A raft is a small boat that you can use to paddle down rivers and streams. Rafting is a good way to experience___2___(natural) . If you want a no...
【单选题】在下列四个命题中 ①已知A、B、C、D是空间的任意四点,则 AB + BC + CD + DA = 0 . ②若{ a , b , c }为空间的一组基底,则{ a + b , b + c , c + a }也构成空间的一组基底. ③ |( a ? b )|? c =| a |?| b |?| c | . ④对于空间的任意一点O和不共线的三点A、B、C,若 OP =x OA +y OB +z OC...