Explanation:
Comparative degree is used to compare two things or actions. In this case, we are comparing the ability of the speaker and the professional runner to run. The sentence suggests that the professional runner is better at running than the speaker.

Comparative Degree:
The comparative degree is used when we are comparing two things or actions. It is formed by adding "-er" to the end of the adjective or by using the word "more" before the adjective. In this case, the adjective "better" is used to compare the ability to run.

Use of "Far" and "Very":
Option 'C' ("far") and option 'D' ("very") are not suitable in this context. The word "far" is used to indicate a large distance or a significant difference. It does not convey the idea of comparison in this sentence. The word "very" is an adverb used to intensify an adjective or another adverb. It does not indicate comparison between two things.

Professional Runner:
The sentence states that the person being compared is a professional runner. This means that they have extensive experience and training in running. It is logical to assume that a professional runner would be better at running than someone who is not a professional.

Choice of Option 'B':
Option 'B' ("more") is the correct answer because it is used to form the comparative degree of the adjective "better". It is the appropriate word to indicate comparison between the abilities of the speaker and the professional runner.

Therefore, the correct answer is option 'B' ("more").