This question has no answer because it does not give any information on the letter, Juans situation, or anything other than the fact that he is sending a letter
Active words are used when the person speaking them is doing the action I.E I threw the ball.
Passive is the opposite. It is used when the subject of the sentence has had something happen to it by someone or something else.
Mango was a rlly nice doggie and he played lots of catches
Astrobiology = exobiology // Astrobiology is an important aspect of the space exploration field.
geology = geoscience // We can study the structure, evolution and dynamics of the Earth through geology.
regolith = blanket rock // Regolith lies like a blanket over unfragmented rock.
microbial = microorganism // Skin is a major source of microbial contamination during a surgical procedure.
