This problem is in Contest(s) below:
Contest 1135:入门训练2
Contest 1337:2019好嗨哟
Contest 1098:初一小朋友语法过关练习题
Contest 1048:寒假训练
Contest 1091:初一小朋友语法过关练习题
Contest 1177:初一小朋友训练
Contest 1342:数论的题
Contest 1332:2019小六训练题集
Contest 1211:复习赛
Contest 1162:初一小朋友寒假作业