Why do countries face challenges to development?

answer is d. graphite coatings.

some connecting rods have _graphite coatings_ to lubricate the cylinder wall or piston pin.

the atmosphere, the biosphere, the hydrosphere, and the lithosphere.   are all physical systems is probably

the correct answer is:

b. substitution property.

if the circle m is with inscribed ∠kjl and congruent radii jm and ml then m = ∠mjl = (kl) because of the substitution property.