The answer is vaccination! hope this helped ;)
The root word which means "red" is a. erythr/o.
Just think about biology - you should know that red blood cells are called erythrocytes, where you can obviously see that root word.
Leuk/o refers to white color, and the other two options do not refer to colors at all.
Walk more, cook food from scratch, make own sauces with less sugar and salt, cut out processed food, grow own veggies,
