题目下列函数是对数函数的是()A. y = 2 ln xB. y = log_2 x^2C. y = ln (2x)D. y = lg x下列函数是对数函数的是()A. $y = 2 \ln x$B. $y = \log_2 x^2$C. $y = \ln (2x)$D. $y = \lg x$题目解答答案D. $y = \lg x$