I need help with my math but you can only choose one correct answer​

Iknow the answer is a but i don't know why

Three cards with holes are arranged in a straight line. a light is shined through the first card’s hole and travels through all three cards. what does this tell you about light rays? a) that light is reflected b) that light is refractive c) that light travels in a straight line d) that light does not travel in a straight line

How have the greenhouse gasses increased from the year 2000 to 2018