Answer:
The answer to your question would be that the sentence that is written correctly is the following one: My garden has green peppers, carrots, and three different kinds of tomatoes.
Explanation:
The sentence is an example of the use of the comma. You should use commas to separate words and word groups in a simple series of three or more items. In this case, it lists the greens that the person has in in his/her garden.
