Đáp án đúng: B
Giải chi tiết:\(\begin{array}{l}{49.7^x} = 2401\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,{7^x}\,\, = 2401:49\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,{7^x}\,\, = 49\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,{7^x}\,\, = {7^2}\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,x = 2.\end{array}\)
Vậy \(x = 2.\)
Chọn B.