How to properly use and punctuate a adjective clause to combine sentences?

An adjective clause does not express a complete thought, so it cannot stand alone as a sentence. To avoid writing a fragment, you must connect each adjective clause to a main clause. For each sentence, you will have to decide if the adjective clause is essential or nonessential and then use commas accordingly. Essential clauses do not require commas. An adjective clause is essential when you need the information it provides. Look at this example:

The vegetables that people leave uneaten are often the most nutritious. If, however, we eliminate vegetables and choose a more specific noun instead, the adjective clause becomes nonessential and does require commas to separate it from the rest of the sentence: Broccoli, which people often leave uneaten, is very nutritious.