Answer:
3. Our teacher Miss Allen, is very good
Step-by-step explanation:
Looking at these answer choices, there seems to be two different instances in which we need commas. First, whenever a proper name of someone is being identified. In these answer choices, the teacher is being identified as Miss Allen. When this is happening, her name should be between commas. Here's an example of what this looks like in another sentence:
"My neighbor, Jennifer, is very kind."
The name Jennifer in that example must be with commas since she is being identified with her proper name.
Second, any interruptions within sentences should have commas since they are disrupting the main idea of the sentence. In these answer choices, the term, " who is our teacher," is interrupting the main idea, therefor requiring commas. Here's an example of what that would look like:
"My cat, who's very grumpy, bit me earlier."
"Who's very grumpy," would be the interruption in that sentence!
Finally, we can apply this knowledge to our answer choices to find out which one is missing a comma. In the first two choices, our interruptions both have commas around them, so they are not missing any. The third choice has a comma after, "Miss Allen," but it also needs one before it. The fourth choice uses a proper comma with the proper name, so the only choice that is missing a comma is choice 3. That sentence, if correct, would read, "Our teacher, Miss Allen, is very good."