①该函数的值域为［-1，1］；②当且仅当x=2kπ+(k∈Z)时，该函数取得最大值1；

③该函数是以π为最小正周期的周期函数；④当且仅当2kπ+π＜x＜2kπ+(k∈Z)时,f(x)＜0.上述命题中错误命题的个数为

A.1                   B.2                     C.3                     D.4

A.-297                   B.-252                   C.252                  D.207

A.2                    B.-                 C.-                  D.1

A.2条                  B.3条                 C.4条                 D.无数条

①l₁、l₂都平行于同一平面  ②l₁、l₂与同一平面所成角相等  ③l₁平行于l₂所在平面  ④l₁、l₂垂直于同一平面

A.1                 B.2                 C.3                  D.4

A.                  B.-                   C.2                D.-2

A.m=1或m=-2                          B.m=1

C.m=-2                                    D.m的值不存在

A.2-              B.              C.2±          D.2+

A.-2                  B.9                    C.6.5                  D.18

A.充分不必要条件                     B.必要不充分条件

C.充要条件                              D.既不充分又不必要条件