设(X，Y)服从二维正态分布，其边缘分布为X～N(1，1)，Y～N(2，4)，X，Y的相关系数为p_xy=-0.5，且P(aX+bY≤1)=0.5，则(  )．

A x=0与x=1都是f(x)的第一类间断点． B x=0与x=1都是f(x)的第二类间断点． C x=0是f(x)的第一类间断点，x=1是f(x)的第二类间断点． D x=0是f(x)的第二类间断点，x=1是f(x)的第一类间断点．

A 高阶无穷小 B 低阶无穷小 C 同阶但非等价的无穷小 D 等价无穷小

A f(x)=|x|sin|x| B <img width="218" height="22" src="https://www.beizhujiaoyu.com/uploads/202208/20210917234739_1638.jpg" /> C f(x)=|x|cos|x| D <img width="176" height="22" src="https://www.beizhujiaoyu.com/uploads/202208/20210917234739_5711.jpg" />

A 0个 B 1个 C 2个 D 3个

A -2   B -1   C 1   D 2

A 1 B <img width="19" height="40" src="https://www.beizhujiaoyu.com/uploads/202208/20211031002155_8835.jpg" /> C <img width="24" height="20" src="https://www.beizhujiaoyu.com/uploads/202208/20211031002157_7596.jpg" /> D <img width="25" height="48" src="https://www.beizhujiaoyu.com/uploads/202208/20211031002158_1035.jpg" />

A (-2，2) B 2 C (2，+∞) D (-∞，-2)

A <img width="151" height="46" src="https://www.beizhujiaoyu.com/uploads/202208/20210917223625_6058.jpg" /> B <img width="179" height="46" src="https://www.beizhujiaoyu.com/uploads/202208/20210917223626_0893.jpg" /> C <img width="80" height="46" src="https://www.beizhujiaoyu.com/uploads/202208/20210917223627_7133.jpg" /> D <img width="108" height="46" src="https://www.beizhujiaoyu.com/uploads/202208/20210917223628_2612.jpg" />

A <img width="74" height="21" src="https://www.beizhujiaoyu.com/uploads/202208/20211118123937_0709.jpg" /> B <img width="115" height="37" src="https://www.beizhujiaoyu.com/uploads/202208/20211118123938_6334.jpg" /> C <img width="115" height="37" src="https://www.beizhujiaoyu.com/uploads/202208/20211118123939_2584.jpg" /> D <img width="115" height="37" src="https://www.beizhujiaoyu.com/uploads/202208/20211118123940_8990.jpg" />