Sentence Correction (SC) | Re: Based on meticulous research over a 10 year period, a group of climate

Based on meticulous research over a 10 year period, a group of climate scientists have determined that methane is accumulating in the atmosphere much faster than previously believed.

A. Based on meticulous research gathered over a 10 year period, a group of climate scientistshave determined - a group of scientists is a singular subject so the verb should be "has"
B. Based on meticulous research gathered over a 10 year period, a group of climate scientists has determinedclose. correct verb but this is a dangling modifier