Select all that apply to colloids.
a.) a colloid is a mixture intermediate between heterogeneous and homogenous. b.) colloids cannot be separated by filtration.
c.) colloids can be seen using an optical microscope.
d.) fog and smoke are examples of colloids.
e.) the tyndall effect is a test to determine whether or not a mixture is a colloid.

The following applied to colloids:
1. They can not be separated by filtration. This is because colloids are uniform and homogeneous in nature. They do not produce sediments when left standing.
2. Colloids can be be seen using optical microscope. This is because, the diameter of the dispersed particles range from 1 to 1000 nanometer. This size range can easily be seen under optical microscope.
3. Fog and smoke are example of colloids. Smoke is a type of colloid in which solid is dispersed in gas while in fog, liquid is dispersed in gas. 
4. The Tyndall effect is a test that determine whether or not a mixture is a colloid. Light is dispersed by colloidal particles. 

They did not study the continental drift

North atlantic current or north atlantic drift is the answer