The observations for each test are:
A: Br$_2$ water test indicates unsaturation (reddish orange color disappears).
B: Ceric ammonium nitrate test detects alcohols (red color appears).
C: Ferric chloride test detects phenols (blue, green, violet, or red color appears).
D: 2,4-DNP test detects aldehydes/ketones (yellow-orange precipitate).
The velocity-time graph of an object moving along a straight line is shown in the figure. What is the distance covered by the object between \( t = 0 \) to \( t = 4s \)?