The main way constitutional amendments are proposed is by
a convention requested by a majority of state legislatures.
a convention requested by the three branches of government.
a vote of three-fourths of both chambers of congress.
a vote of two-thirds of both chambers of congress.

The answer is a vote of two-thirds of both chambers of congress

The Correct Answer is

A vote of two-thirds of both chambers of Congress.

Explanation:

The Constitution can not be changed by any single entity, this document is very complex to change or amend but it could be amended in various ways. The Constitution grants that an amendment may be recommended by the house of the Senate and the House of Representatives, each house of the Congress with a two-thirds majority of the voting strength in both or by a constitutional convention invited by two-thirds of the legislature of states.