XY09-41 so的指代

请问这里so只带什么东东？应该怎么选择？

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Q41:

The first English settlers to establish a permanent colony in America did it not at Plymouth but along the shore of the James River west of Chesapeake Bay.

1. it not at Plymouth but

2. so not at Plymouth but

3. not at Plymouth but instead

4. not at Plymouth but did so

5. it not at Plymouth but rather