have to 否认构造是don't(doesn't) have to;before three days 应该是three days before 吧？three days before一般后面还要加时间，在……的三天前，而three days ago 指的是今天年起的三天前
1, have to的否认式是：（do/does) not have to.
2，before three days为‘三天前’，多用于过往完成时态中。而three days ago是‘从如今起，向前数三天’，只用于一般过往时态。
1.不是.应为nothaveto2.一样
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