下列命题中,真命题的个数是( ) ①若“p∨q”为真命题,则“p∧q”为真命题; ②“∀a∈(0,+∞),函数y=在定义域内单调递增”的否定; ③l为直线,α,β为两个不同的平面,若l⊥β,α⊥β,则l∥α; ④“∀x∈R,≥0”的否定为“∃∉R,<0”. A. B. C. D.() 17. (2013 河南) 一Dad,must we wait until the light becomes green? —Yes,I'm afraid we . That's the traffic rule. A. can B. may C. have to D. need