题目

--- Argon, can I borrow your textbook? --- Sorry, not _____ you help make a note of what the teacher says. A. unless       B. if        C. when      D. since 答案：A14．某人定制了一批如图所示的地砖，每块地砖都是边长为（x+3y）米的正方形，点E在正方形ABCD的边BC上，EC=（x+y）米，已知x+3y=5米，x+2y=4米，求四边形AECD的面积．