Answer:
Some (most) has two tails.You can see the tails when the comets go near the sun.There are two types of comet tails,dust and gas ion. Comet tails can be over 600,000 miles (1 million km) long.Because the comet dust particles are so small, they are pushed away from the Sun into a long tail.They are made of ices, such as water, carbon dioxide, ammonia and methane, mixed with dust.There are so much more to discover about comets (which I might not know).
Hope that was helpful.Thank you!!!