【简答题】关于直线 m 、 n 和平面 a 、 b 有个命题: ①当 m ∥ a , n ∥ b , a ∥ b 时, m ∥ n ②当 m ∥ n , m Ì a , n ⊥ b 时, a ⊥ b ③当 a ∩ b = m , m ∥ n 时, n ∥ a 且 n ∥ b ④当 m ⊥ n , a ∩ b = m 时, n ⊥ a 或 n ⊥ b , 其中假命题的序号是 。
【单选题】" In China it is relatively usual to ask people their age, but in the West this question is generally regarded as impolite. This is particularly true 56 women, and even more 57 if the inquirer is a ma...