This problem is in Contest(s) below:
Contest 1169:基础班第二周
Contest 1044:2019夏令营基础一班3.1
Contest 1070:11.22作业
Contest 1087:区三中周六上午测试
Contest 1068:11.22课堂练习
Contest 1096:基础1班14号晚训练
Contest 1231:史口中学
Contest 1315:史口中学
Contest 1978:零基础第三节
Contest 1978:零基础第三节