The combination of your taste buds and the smell of food is what makes your brain recognize a taste. When you have a cold, your nose gets clogged and you can't smell as well as you normally can, so in your head, foods don't taste the same because you're not getting the normal amount of "taste information" from your nose".
Genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).
Answer:
The thymus
Explanation:
It is the most active and starts making T-cells before you are even born. After puberty the thymus shrinks and is replaced with fat.