Let's start by saying each of the answer choices out loud:

Rake

Make

Mate

Sad

Now, let's look at the vowels in each of the words.

Rake

Make

Mate

Sad

All of the vowels are the letter a, but do they all sound the same? No, they do not.

Rake, make, and mate all have a long vowel sound.

Sad has a short vowel sound. Since only one of the words has a short vowel sound, that is the word that does not belong with the others.