Use the dictionary entry for crude to answer the question.

crude

crude [‘krüd] adj

from latin crudus

1. the quality of being unchanged from the original state

2. the quality of being primitive or uncultured

3. the quality of being obvious

4. the quality of being rough in execution

which word best defines the word crude?

polished
undeveloped
skilled
mature

The word that best defines the word crude is undeveloped. If you take a look at those dictionary definitions that you've been given, you'll see that the word undeveloped is the only one that makes sense here. The other words, polished, skilled, and mature have nothing to do with those explanations and as such pretty much have the opposite meanings of the word crude, making them its antonyms, not a synonym which undeveloped is.