Tú casa es grande.

The difference between "tú" and "usted" depends on the formality. "Tú" is used <u>when talking to friends or relatives (informal)</u> while "usted" is used <u>when talking to older people or a person of high social rank (formal)</u>.
In this case we want to write the <u>informal</u> form of "tú", so we use "tú". Also, when dealing with <u>permanent states</u>, the verb "ser" (to be) is used.
Answer:
Explanation:
When passengers wait at the gate, do they look at their boarding pass?
The correct answer is not A. Im sorry to say this but the correct answer is B. por la puerta de embarque (which will by by the gate). If you use the A option there would be a grammatical mistake putting the word "por" before something that makes no sense. Im a native spanish speaker and a teacher so believe the better way to say is por la puerta de embarque