Which choice completes the text so that it conforms to the convention…

Source Texts

Text

Dong Lai and Diego J. Muñoz's work on circumbinary disk accretion-a process in which, due to gravity, material from an orbiting disk spirals inward and accumulates onto two stars or black holes-relies heavily on simulations. Lai and Muñoz recognize the need for direct ________ recommending evolving binary star systems as a promising avenue for future study.

Which choice completes the text so that it conforms to the conventions of Standard English?

observation, however,

observation; however,

observation. However,

observation, however;