Cousteau and Gagnan:

A. invented SCUBA

B. lived in Sealab ||

C. developed "significant wave" theory

D. created a self-contained diving vessel called Trieste

The answer is A. Invented SCUBA

Explanation:

Emile Gagnan and Jacques Cousteau were engineers who invented the first SCUBA device, the Aqua-Lung. Gagnan's most important contribution to this discovery was his theory that a valve commonly used in gas generator engines would be useful in regulating air supply under water in varying pressures.