Convection currents within earth's core and mantle transfer large amounts of heat when
a. hotter, less dense rock rises and cooler, more dense rock sinks
b. cooler, less dense rock sinks and hotter, more dense rock rises
c. hotter, less dense rock sinks and cooler, more dense rock rises.
d. cooler, less dense rock rises and hotter, more dense rock sinks.

its c

Explanation:

c.) hotter,less dense rock sinks and cooler, more dense rocks rises

d₁ = displacement of tern from arctic to antarctic = 11000 miles

d₂ = displacement of tern from antarctic to arctic =   - 11000 miles

d = total displacement for the journey

total displacement for the journey is given as

d = d₁ + d₂

d = 11000 + (-11000)

d = 0 miles

t₁ = time of travel from arctic to antarctic = 3 months = 3 x 30 days = 90 days

t₂ = time of travel from antarctic to arctic = 3 months = 3 x 30 days = 90 days

t = total time of travel

total time of travel is given as

t = t₁ + t₂

t = 90 + 90

t = 180 days

average velocity is given as

average velocity = total displacement/ total time

v = d/t

v = 0/180

v = 0 miles/day