题目

Robert is said _______abroad, but I don't know which country he studied in. A . to have studied B . to study C . to be studying D . to be studied 答案：A化学方程式a C2H2+ b O2c H2O + d CO2配平后a、b、c、d之和为 (   )A. 13 B. 14 C. 15 D. 10