Most sociologists view race as meaningful in the sense that it is a category'

The correct answer is known as "social".

A social category is considered to be a group of people, who does not really interact with one another, yet they share the same characteristics or aspects. An example of a social category is the elderly people, wherein they do not interact mostly, but they do share the same characteristics of being an old person.

Scientists don't disagree over the occurrence of global warning: there is a significant amount of evidence for global warning, and it is considered to be established.- we can reject answer b) and d) together with it

Also it is established that humanity must do something to combat climate change. - so we also reject answer c)

we are now left with answer a) - they disagree in the rate of global climate change. This is however not strictly true - there might be some disagreement about the exact rate, the disagreement is not big. It's the best answer, but it's also not very fortunate.