1.What did many Anti-federalist conclude after they studied ancient Greek and Roman republics?

The correct answer to this open question is the following.

Many Anti-federalists concluded that the United States needed a free republic as a model for the new government after they studied ancient Greek and Roman republics.

Antifederalists did not agree on the idea of having a strong central government as the Federalists proposed. Antifederalists argued that a strong federal government could turn into tyranny, as was the case of the English monarchy. So during the Constitutional Convention in the city of Philadelphia, Pennsylvania, Federalists led by Alexander Hamilton and Jhon Jay, debated and argued with Antifederalists who supported a simpler form of government that included rights for their citizens, influenced by the ancient Greek form of Democracy or the Roman Republic.

explanation:

there are two statements that are incorrect.

1. the marshall plan was a lend lease program. it was an economic plan that europe redevelop itself after wwii.

2. einstein didn't really do anything to further the allied cause in building the bomb. he merely sent a letter to fdr telling him (in 1939) that if the united states entered the war, perhaps it would be wise to build the bomb before germany did. i would say this answer is incorrect, but when america entered the war 2 years later, fdr thought it might be a good idea to take einstein's advice.

the 4th choice is definitely so wrong that is likely the single answer of this question

monasticism. people often do monasticism in monasteries