The suffix "-ity" often combines with adjectives to form nouns. Nouns formed in this way refer to the state or condition described by the adjective, for example, intensity.
【单选题】有下列命题: 1 若直线 l 平行于平面 α 内的无数条直线,则 l ∥ α ; 2 若直线 a 在平面 α 外,则 a ∥ α ; 3 若直线 a ∥ b , b ∥ α ,则 a ∥ α ; 4 若直线 a ∥ b , b ∥ α ,则 a 平行于平面 α 内的无数条直线. 其中真命题的个数是 ( )