47. Which of the following descriptions as to theophylline is RIGHT ? (A) The structure left is theophylline. (B) Theophylline is a trimethylxanthine. (C) Theophylline is the hypoxanthine derivative of tea. (D) Theophylline is similar with caffeine but lack the methyl group at N-1 of the heterocycle. (E) None of them.