I am also very good at working with people, as I am naturally outgoing and friendly. Which word or phrase synonym of the word skillful is the most appropriate substitution for the underlined phrase? A. able B. effective C. masterful D. up to speed

The most appropriate word that could substitute 'skillful' would be C. masterful

The world skilfull in this particular context means having the ability to do something with a certain amount of expertise.

The word masterful have a similar meaning because it indicates the person able to do that certain thing with higher than average virtuoso.

C, masterful is a synonym of skillful