A study was conducted to investigate adults in Chicago, USA in 2020. The study wanted to investigate if learning ability could be affected by different environmental conditions at the "Smell and Taste Treatment and Research Foundation". 200 randomly selected people from Chicago in 2020 worked through one set of pencil and paper maze and the times taken were recorded. Data were collected for the following variables: Variable Description Gender: male, female Smoke: smoker, non-smoker Age: Age of participant in years Time: Time to complete the maze, in seconds (a) Choose the right classification for the four variables above. [2 marks]