The correct answer is A) the Senate must approve them.
A limitation on the president’s power to appoint ambassadors is that the Senate must approve them.
In the United States political system, ambassadors are appointed by the US President but are confirmed by the members of the Senate. If an ambassador is appointed durn Congress recess, the Ambassador can only serve until the end of the next session inCongress, except the Senate confirm it. Ambassadors represent the interests of the United States in many countries and are the diplomats that negotiate foreign relationships with these countries. That is why the position -so important- must be confirmed by the Senate.