Question

in anaerobic respiration
water is a reactant
oxygen is absent
oxygen is present
lactic acid is a reactant

Explanation:

Anaerobic respiration occurs without oxygen. Water is not a reactant in the basic anaerobic - respiration process. Oxygen is absent, not present. Lactic acid can be a product in some forms of anaerobic respiration (like in muscle cells), not a reactant.

Answer:

oxygen is absent