What are the four bases of DNA?

Would really appreciate it, i have an idea but not completely sure

Johnny rode his bike 4 blicks down the street to his friend's house once he got to his friend house and realized he could not cone out to play he turned aroubd and went back home.what is displacement for the total bike ride? how did you determine this? what could we use as a reference point to determine he was in motion during his bike ride? why can you use it as a reference point

Most crimes involve some evidence relating to the human body; for that reason, what related science is frequently used in forensic investigations? a)psychiatry b)physics c)botany d)biology