Why did the Framers of the Constitution give the president the sole power to fire people in the State Department?

Why did the Framers of the Constitution give the president the sole power to fire people in the State Department?

a. The president needs to be able to rely on people who give him information about foreign governments so that he can swiftly.

b. They felt that countries needed to see that the president is strong.

c. They wanted to prevent the president from acting like a king.

d. They thought that the Senate's ability to give consent to the nomination was a sufficient check on presidential power.