The correct answer is B.

Explanation: The word "dominant" refers to someone who has control or influence over others, particularly in a certain context or industry.

- B. An influential is the nearest in meaning to "dominant," as it conveys the idea of having significant power or control, which aligns with the concept of dominance.

Other options:
- A. An important: While "dominant" implies importance, it specifically refers to having influence or control, which is more precise than just being important.
- C. An outstanding: This means distinguished or excellent, which does not necessarily convey the sense of control or influence.
- D. A prominent: This means well-known or easily noticeable, which is related but not as specific about having control or influence as "dominant."

Thus, "influential" is the option that best matches the meaning of "dominant."