How long human can live inside the water without oxygen?

What is the earliest point in the universe that we can observe? why can’t we see back further than this?

For general projectile motion, when the projectile is at the highest point of its trajectory, its acceleration is zero? a)the horizontal and vertical components of its velocity are zero. b) its velocity is perpendicular to the acceleration. c)the horizontal component of its velocity is zero. d)its velocity and acceleration are both zero.

What is a carrier wave and how does it affect what you hear on the radio