题目3单选题
[定积分的定义] 由<img src="https://tihai-oss-cloud.itihey.com/img/7b3183f3599fa63babe687120bf6dbd4.png">围成的平面图形的面积为A. <img src="https://tihai-oss-cloud.itihey.com/img/ceb6fc48e775dc83360a84720d451cd5.png">B. <img src="https://tihai-oss-cloud.itihey.com/img/7c3da3dcfcf75db18cfa288d081b4067.png">C. <img src="https://tihai-oss-cloud.itihey.com/img/3e10885631533c95aef3a0132cc4d430.png">D. <img src="https://tihai-oss-cloud.itihey.com/img/4ebc31d4babb8742a0ac18fedd2af593.png">