题目

请列举一个单项式，使它满足系数为2，次数为3，含有字母a、b，单项式可以为     . 答案： 2ab2或2a2bTo keep fit, you should take more______ . Don’t be always busy doing your ______.A．exercise; exerciseB．exercises; exercisesC．exercises; exerciseD．exercise; exercises