Pls hurry, i'm timed TmT Read this excerpt from "Why Are They Called Black Holes?"

Black holes are invisible because they have so much gravity that nothing escapes. Not even light can escape or bounce off. So how do scientists know that black holes exist if they are invisible?

Gravity is caused by matter, and as matter increases, the pull of gravity increases too. Stars are born when enough matter collects that gravity makes it collapse into a hot, dense protostar.

According to the introduction, why are black holes invisible?

Scientists can not figure out why they exist.
Gravity is caused by matter.
They have so much gravity that nothing escapes.
Stars are created first.

To understand the electric potential and electric field of a point charge in three dimensions consider a positive point charge q, located at the origin of three-dimensional space. throughout this problem, use k in place of 14? ? 0. part adue to symmetry, the electric field of a point charge at the origin must point from the origin.answer in one word.part bfind e(r), the magnitude of the electric field at distance r from the point charge q.express your answer in terms of r, k, and q. part cfind v(r), the electric potential at distance rfrom the point charge q.express your answer in terms of r, k, and q part dwhich of the following is the correct relationship between the magnitude of a radial electric field and its associated electric potential ? more than one answer may be correct for the particular case of a point charge at the origin, but you should choose the correct general relationship. a)e(r)=dv(r)drb)e(r)=v(r)rc)e(r)=? dv(r)drd)e(r)=? v(r)r