在下列各溶液中，离子一定能大量共存的是[ ]

A．强酸溶液中：K⁺、Fe²⁺、MnO₄^-、SO₄^2-

B．含有0．1mol·L^-1HCO₃^-的溶液中：K⁺、Ca²⁺、OH^-、NO₃^-

C．含有0．1mol·L^-1Cu²⁺的溶液中：Na⁺、K⁺、S^2-、SO₄^2-

D．室温下，pH=14的溶液中：Na⁺、K⁺、NO₃^-、CO₃^2-

John _____ knowledge of radio just by staying around the radio station. [ ]

A. caught on

B. worked up

C. took up

D. picked up