What is an executive agreement?
a. pact with congress and foreign heads of state
c. pact amongst heads of state
b. pact with the president and congress
d. pact with president and foreign heads of state

An exceutive agreement is:

D) pact with president and foreign heads of state

An executive agreement is an international agreement. It is made by the executive branch of the US government without ratification by the Senate-- which means that the Senate does not get to confirm something (usually by voting) for a proposed law. 

Hope this helps! ☺