The correct option is A Naphthalene acetic acid
Auxins are of two types - natural and synthetic auxins.
Natural auxins are obtained from plants. E.g., indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), 4-chloroindole-3-acetic acid (4-Cl-IAA), etc.
Synthetic auxins are artificially produced compounds that function as auxins. E.g., naphthalene acetic acid (NAA), 2,4-dichlorophenoxy acetic acid (2,4-D), etc.