If pq and rs intersect to form four right angles, which statement is true?
a. pq + rs
b. pq and rs are skew
c. pq and rs are parallel
d. pq= rs

This is all you, but i can give you some topics that you could try. if it rained when you want to do something outdoors, it 'limits' that human activity. maybe you want to do an experiment that goes throughout the whole year and you have to have above freezing the entire year. this 'limits' your activity. i thought of those just off of the top of my head. something that gets to me that might be getting to you is you are thinking too hard about what to do. think simply, and if it is too simple, then bump it up just a little bit.

According to new research, more than 5..5 million deaths are associated with polluted air. hope this : ).

The circumcenter is  equidistant  from each vertex of the triangle. the circumcenter is at the  intersection  of the  perpendicular bisectors  of the triangle's sides. the circumcenter of a right triangle falls on the side opposite the right  angle. the incenter  of a triangle is always inside it.