Question 20 ocean currents do not move in straight lines; instead, they curve as they cross the planet. what is responsible for these patterns of movement? differences in water salinity differences in water density the rotation of the earth differences in water temperature

Ocean current movement is affected mostly by five things: gravity, salinity, temperature, wind(Coriolis effect), and natural events such as earthquakes. However, the factor which makes it move in a curved pattern is the Coriolis Effect (phenomenon brought by the rotation of the Earth).  

Wind(Coriolis Effect) - Due to the Earth's rotation, wind moves towards the right in the Northern Hemisphere and towards the left in the Southern Hemisphere. These global winds dragging on the surface of the water drive the movement of the ocean currents. 

81 is a composite number