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
The answer is: <span>The </span>unit of measure concept<span> is a standard convention used in accounting, under which all transactions must be consistently recorded using the same currency.</span>
Vamos
we are going to a have a class about conquistadors.
The mouse because mouse in Spanish is ratón
