Which of the following is not a suggestion for a sustainable city?

Rooftop gardens
Bicycle programs
recycling already once used water
Food insecurity

The speed of light in a material is 0.50 c. what is the critical angle of a light ray at the interface between the material and a vacuum?

Because light travels in a straight line and casts a shadow, isaac newton hypothesized that light is

Estimate the schwarzschild radius (in kilometers) for a mini-black hole formed when a superadvanced civilization decides to punish you (unfairly) by squeezing you until you become so small that you disappear inside your own event horizon. (assume that the your weight is 50 kg)