Most fish do not sink in water because of the presence of

Most fish do not sink in water because of the presence of
(1) swim bladder
(2) air bladder
(3) air sacs
(4) air in spongy bones

Which of the above options are right:
A) I & II
B) II & III
C) III & IV
D) I, II, III & IV

Answer: A) I & II