Which of the Following Are True About Air-Entrainment Systems

Which of the following are true about air-entrainment systems?
1) Their FiO₂ values are directly proportional to their total flow.
2) They can provide variable FiO₂ values under some clinical conditions.
3) They always deliver O₂ concentrations less than 100%.
4) They yield a set FiO₂ only if their flow exceeds the patient's.

A) 1 and 3 only
B) 1, 2, and 3 only
C) 3 and 4 only
D) 2, 3, and 4 only