【简答题】由空间向量基本定理可知,空间任意向量 p 可由三个不共面的向量 a , b , c 唯一确定地表示为 p =x a +y b +z c ,则称(x,y,z)为基底 < a , b , c > 下的广义坐标.特别地,当 < a , b , c > 为单位正交基底时,(x,y,z)为直角坐标.设 i , j , k 分别为直角坐标中x,y,z正方向上的单位向量,则空间直角坐标(1,2,3)在基底 < ...
【单选题】Natural flavorings and fragrances are often costly and limited in supply. For example, the vital ingredient in a rose fragrance is extracted from natural rose oil at a cost of thousands of dollars a p...
A.
natural flavorings and fragrances are not quite dear
B.
the limitation of natural flavorings and fragrances is clear
C.
the supply of natural flavorings and fragrances is adequate to meet the demand
D.
the cost of producing natural flavorings and fragrances is high
【简答题】Questions 16 to 20 are based on the following passage. The destruction of our natural resources and contamination of our food supply continue occur, largely because of the extreme difficulty in affixi...