Why do you have to put el at the end of a word without an a at the end of the word?

In Spanish, words can be of 2 genders: masculine or feminine. The "la" article is used for feminine nouns (la escuela, la taza, etc), and the "el" article is used for masculine nouns (el hotel, el supermercado, etc).
If the noun ends in -a, it is probably feminine (there are exceptions, such as el mapa and el agua, but this is generally the rule).

The answer is c because i looked it up

The answer is b because it’s los amigos . los amigos is plural and dicen is plural and masculine .