Convection can occur in which two substances?
a) wood and air
b) ice and wood
c) water and ice
d) air and water

Convection can't occur in solids because the atoms in a solid objects cannot move from where they are and that's needed in the process of convection, so that rules out wood and ice so the answer is D) air and water.

molecules are free to separate from each other and will take on the shape of the container. molecules move completely at random and high speeds. they vibrate in a fixed position and do not move around much. molecules expand to the edge of their container.

r = ρ x length / area  

ρ = r x area / length  

ρ is in ohm-meters  

in basic units, it is m³kg/s³a²  

i think this is it.