Answer:
The young project manager lacked communication skills, but he was intelligent, well-spoken, and precise
Step-by-step explanation:
Comma is used to indicate break between the independent clauses. when more than two adjectives are used to qualify the noun then they must be separated by comma. For last adjective and is used but comma is avoided as and serves the purpose to separate them.
In this sentence, before but a comma used as the clause is making complete sense. In next part more than tow adjectives are used therefore first two must be separated by comma and the last one is separated by and.
Now using these rules we see option c is the most appropriate answer