Quotation marks, also called 'inverted commas', are of two types: single and double. British practice is normally to enclose quoted matter between single quotation marks, and to use double quotation marks for a quotation within a quotation:
The oceans absorb the sun's heat, transferring it to the atmosphere and distributing it around the world via the ever-moving ocean currents. This drives global weather patterns and acts as a heater in the winter and an air conditioner in the summer.
What causes ocean currents? A: Wind, temperature differences, water density and salinity all play a role in generating ocean currents. Currents may also be influenced by external forces, such as earthquakes, the coriolis effect produced by the Earth's rotation, and the gravitational pull of the Moon.