You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Catalan_language

Context:
The process of morphological derivation in Catalan follows the same principles as the other Romance languages, where agglutination is common. Many times, several affixes are appended to a preexisting lexeme, and some sound alternations can occur, for example elèctric [əˈlɛktrik] ("electrical") vs. electricitat [ələktrisiˈtat]. Prefixes are usually appended to verbs, for as in preveure ("foresee").

Question:
What word supplement  can be put on an already existing word base?

affixes