899 - Logical Reasoning

Question: Acme brand aspirin claims to be the best headache relief available on the market today. To prove this claim, Acme called 10 people and asked them their thoughts on headache relief products. All 10 of them stated that they unequivocally use Acme brand aspirin on a regular basis and that they believe it to be the best headache relief available on the market today.
Which of the following would most weaken this argument?

1. Acme brand aspirin is highly addictive.
2. The 10 people called were married to the company's top 10 executives, and they were coached on what to say.
3. Most people choose to suffer silently through their headaches and take no medicines whatsoever.
4. This survey was conducted by an independent company.
5. The 10 people were selected at random.