Euphemisms abound for 'toilet'(which is itself a euphemism). What are some of them? Can you judge them in terms of acceptability for various kinds of social functions and interactions?
【单选题】有下列命题: ①双曲线 x 2 25 - y 2 9 =1与椭圆 x 2 35 +y 2 =1有相同的焦点; ②“- 1 2 <x<0”是“2x 2 -5x-3<0”必要不充分条件; ③若向量 a , b 共线,则向量 a , b 所在的直线平行; ④若向量 a , b , c 两两共面,则向量 a , b , c 一定也共面; ⑤?x∈R,x 2 -3x+3≠0. 其中是真命题的个数( )