Questions: Some patients remembered getting a tick bite. Most patients spent a lot of time outside.

The answer is the first one: Some patients remembered getting a tick bite.

Explanation:

1. Some patients remembered getting a tick bite.

   • This fact is directly relevant because it suggests a possible vector (ticks) for the mysterious illness. If multiple patients recall being bitten by ticks, it provides a strong clue that ticks could be responsible for transmitting the disease.

2. Many patients lived near the town center.

   • This fact is less relevant to the specific cause of the symptoms. Living near the town center does not directly indicate a connection to ticks or any other specific vector.

3. Most patients spent a lot of time outside.

   • This fact is also relevant because spending time outside increases the likelihood of exposure to ticks, which are commonly found in outdoor environments. This supports the idea that ticks could be the cause of the symptoms.

Summary: The two facts that led investigators to believe ticks were causing the symptoms are:

1. Some patients remembered getting a tick bite.
2. Most patients spent a lot of time outside.