users集合中已经存在一条记录{"_id":"1001","name":"Jack"}，下面哪句命令可以成功运行？
A. db.students.insert({"_id":"1001","name":"Rose","age":18})
B. db.students.insert({"_id":"1001","name":"Tom"})
C. db.students.save({"_id":"1001","name":"Tom"})
D. db.students.save({"_id":"1001","name":"Tom",年龄:19})
查找姓名是张三，年龄是20的记录，正确的命令是？
A. db.students.find({"姓名":"张三"})
B. db.students.find({"姓名":张三,"年龄":20})
C. db.students.find({"姓名":"张三" and "年龄":20})
D. db.students.find({"姓名":"张三","年龄":20})
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