Final answer:
In the analogy, 'SIMPLE' is the correct word that relates to 'COMPLEX' as 'RESTRAIN' does to 'RELEASE', because 'SIMPLE' is the opposite of 'COMPLEX' just as 'RELEASE' is the opposite of 'RESTRAIN'.
Step-by-step explanation:
The analogy RESTRAIN is to RELEASE as SIMPLE is to COMPLEX is asking you to identify the word that has a relationship to 'COMPLEX' that is similar to the relationship 'RESTRAIN' has to 'RELEASE'. To 'RESTRAIN' something is to hold it back or limit it, while to 'RELEASE' is to free it or let it go. Therefore, we are looking for a word that means the opposite of 'COMPLEX'. The word 'SIMPLE' is the antonym of 'COMPLEX', representing things that are easy to understand or not complicated, just as 'RELEASE' is the antonym of 'RESTRAIN'.