已知等比数列 {an}\left\{ {a}_{n}\right\}{an} 的前 3 项和为 168, a2−a5=42{a}_{2} - {a}_{5} = {42}a2−a5=42 ,则 a6={a}_{6} =a6= ( )A. 14B. 12C. 6D. 3