"Behind the door" is a complete sentence.

I do not think it is a complete sentence because, what's behind the door?

- three-quarters or two-thirds..

- "the constitution provides that an amendment may be proposed either by the congress with a two-thirds majority vote in both the house of representatives and the senate or by a constitutional convention called for by two-thirds of the state legislatures."

< 3

i think option 3. would be ur best bet and u need to write it urself

have a good day