A would be a short-term energy source. (Please Help!) :)

lightbulb?

Explanation:

a lightbulb will run out but can last a while

1. dermis

2. chemical

3. urine

4. viruses

5. antibodies

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)