Which of the following belong to class osteichthyes?
A. Sea urchin B. Seahorse
C. Flying fish D. Sawfish
E. Dogfish

The correct option is B B & C
The classification of the given organisms are:
i) Sea-urchin (Echinus) – Class-Echinoidea, Phylum-Echinodermata (nonchordate)
ii) Sea-horse (Hippocampus) – Class-Osteichthyes, Superclass-Pisces, Division-Gnathostomata, Subphylum-Vertebrata, Chordata
iii) Flying fish (Exocoetus) – Class-Osteichthyes, Superclass-Pisces, Division-Gnathostomata, Subphylum-Vertebrata, Phylum-Chordata
iv) Sawfish (Pristis) – Class-Chondrichthyes, Superclass-Pisces, Division-Gnathostomata, Subphylum-Vertebrata, Phylum-Chordata
v) Dogfish (Scoliodon) – Class-Chondrichthyes, Superclass-Pisces, Division-Gnathostomata, Subphylum-Vertebrata, Phylum-Chordata