In the united states, congress forbade the use of u. s. ground forces in cambodia and laos authorized covert south vietnamese attacks on north vietnam supported the invasion of laos as a deterrent to communism. gave president nixon the power to expand the war into cambodia. 

The correct answer is letter "A": Forbade the use of U.S. ground forces in Cambodia and Laos.

Explanation:

On April 28th, 1970, U.S. President Richard Nixon (1913-1994) granted permission to American soldiers to invade Cambodia with the justification that it was a decisive step to take in taking down the Communist block in Asia. The Congress of the U.S. never authorized the incursion and accused Nixon of having illegally widened the war.  

Having said this, the correct option is the letter "A", Congress forbade the use of U.S. ground forces in Cambodia and Laos.

d. migration