Which is the best type of scientific investigation for Bena to use to study this?

starchy vegetables are high in carbohydrates.

starchy vegetables contain more carbohydrates than non-starchy vegetables.

explanation:

there are two primary categories of carbohydrates, essentially differentiated on the basis of their carbohydrate content (which is in the form of starch - a complex carbohydrate):

those vegetables which contain little amounts of starch are termed as non-starchy vegetables, and some examples include: artichokes, broccoli and bean sprouts.

vegetables high in their starch content are distinguished as starchy vegetables, and some examples include: potatoes, chickpeas and corn.