有两箱同种零件，第一箱内装50件，其中一等品10件；第二箱内装30件，其中一等品18件；现随机地从两箱中挑出一箱，再从这箱中随机地取出一件零件，则取出的零件是一等品的概率为

A 0．25 B 0．30 C O．35 D 0．40

A 2 B 4 C 8 D 16

A <img src="https://www.beizhujiaoyu.com/uploads/202208/164845008019881.png" width="31" height="32" /> B ln|x| C <img src="https://www.beizhujiaoyu.com/uploads/202208/164845008524741.png" width="40" height="28" /> D cotx

A 1 B <img src="https://www.beizhujiaoyu.com/uploads/202208/164845228378871.png" width="15" height="31" /> C 2 D 不存在

A a<0且c=0 B a>0且c是任意常数 C a<0且c≠0 D a<0且c是任意常数

A 奇函数 B 偶函数 C 非奇非偶函数 D 周期函数

A <img src="https://www.beizhujiaoyu.com/uploads/202208/164844927183691.png" width="60" height="32" /> B <img src="https://www.beizhujiaoyu.com/uploads/202208/164844928043421.png" width="51" height="32" /> C 1+2e2 D 1+e2

A 单调减少 B 单调增加 C 不增不减 D 有增有减

A <img src="https://www.beizhujiaoyu.com/uploads/202208/164845065482921.png" width="163" height="33" /> B <img src="https://www.beizhujiaoyu.com/uploads/202208/16484506631691.png" width="185" height="33" /> C <img src="https://www.beizhujiaoyu.com/uploads/202208/164845066864601.png" width="107" height="33" /> D <img src="https://www.beizhujiaoyu.com/uploads/202208/164845067242611.png" width="242" height="33" />