选出下列每组单词中与其他两项不同类的一项。
①____A.pick B.swim C.summer
②____A.season B.summer C.autumn
③____A.spring B.sometimes C.usually
④____A.often B.always C.spots
⑤____A.sunny B.cake C.rainy
对x∈R,'k∈N+,定义Mxk=xx+1x+2…x+k-1,则函数fx=Mx-5-11·sinx是( )