Which statement is correct? a Star formation begins in the nebula
b White dwarfs become main-sequence stars when they gain mass
c Supergiants are stars that can absorb black holes
d Main-sequence stars are formed by comets

With i really need the correct answer!

How many excess electrons must be present on each sphere if the magnitude of the force of repulsion between them is 4.57×10−21 newtons?

Orque can be calculated by multiplying the force (n) applied at 90∘ to the lever arm at a distance (m) from the pivot point (point of rotation), the compound si unit for the torque is n⋅m. if the force (at 90∘ to the lever arm) applied is 15 n and it is applied at 2.0 m from the pivot point (point of rotation), what is the torque on the lever?