QUESTION $6$

You are writing a research paper on the impacts of hydraulic fracturing $("$fracking$")$ on groundwater in your state. Through your research, you have found that a professor at a university in another state, Dr$.$ Thomas Henry Wright, has conducted extensive research on the subject. You decide to write an inquiry letter to ask him some questions. Which salutation is most appropriate for your letter?

a$.$ Dear Tom:

b$.$ Dear Thomas Henry Wright

c$.$ Dear Dr$.$ Wright:

d$.$ Dear Professor: