Which of the following is the correctly abbreviated S I unit describing The amount of a substance

There are no correct abbreviations on the list of choices that you provided.

It could be one of these (or it could be something else):

- - mL (milliliter)

- - L (liter)

- - cm³ (cubic centimeter)

- - m³ (cubic meter)

It's definitely NOT:

- - gal (gallon)

- - Qt (quart)

- - fl oz (fluid ounce)