题目

已知等差数列的公差为，若成等比数列，则 （   ）A.     B.     C.     D. 答案：【答案】B【解析】由于成等比数列，即， ，解得.—Hi, Jim! What's your plan?—I will be on ____ holiday.A.a two-dayB.a two dayC.a two-day'sD.a two-days