Finding errors in study conclusions

A company tested their new golf ball by having

20

professional golfers each hit

100

shots with the company's new ball and

100

shots with the golfer's current ball (in a random order). The labels were removed, so the golfers didn't know which balls were which. The golfers, on average, hit their shots significantly farther with the new ball.

The company cites this study in an advertisement claiming that this new ball will help all golfers hit farther shots.

Why is the company's claim not appropriate?

(Choice A)
The study was an experiment, but it only included professional golfers.
(Choice B)
The study was an experiment, but it didn't group the golfers into blocks based on their abilities.
(Choice C)
The study wasn't a census, which is the best way to establish causation.
(Choice D)
The study was observational, so they shouldn't make a causal conclusion.
(Choice E)
The study was observational, so the sample size isn't large enough to support their claim.

High school statistics

Course: High school statistics > Unit 5

Problem