Trouble with Entities

I am having some trouble distinguishing the different entities...

Which one protects the owner from the general obligations of the business?
Which entity only taxes the profits of the business one time?
Which one is available for businesses with a single owner?
Which one is required to file an annual tax return?

I was thinking...
1. LLC
2. C corporation
3. sole proprietorship
4. all of them

Is this correct?

Which jurisdiction are you in?

idk. I just had the options sole proprietorship, C corporation, S corporation, partnership, LLC, and LLP.

Does anyone know the answer to these?

A sole proprietor remains liable for the GO of the business so this fails the first question.
A C Corp pays taxes at the corporate level and again after distributing to the owners so this fails the second question.
A corp pays quarterly taxes so it fails the last question.

A LLC has limited liability and is considered a disregarded tax entity so taxes are only assessed on the individual's return. Taxes are only filed annually as part of the individual's taxes. An LLC can be just a single owner. Therefore, I believe the answer is LLC.

I think I misread your question as each question is invidividually answered. I woudl respond

1. LLC, Corp, C Corp
2. LLC
3. Sole Prop, LLC, Corp
4. All