Why did president Johnson believe that it was important for the United States to win in Vietnam?

To stop the spread of communism

Explanation:

The USA got involved in the war of Vietnam,

so that communism wouldn't spread, Johnson was afraid

that if Vietnam was taken by communist government it would keep

spreading downwards towards the USA.

the answer is option a.

- 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