Answer:
I believe the first option could be effective.
Step-by-step explanation:
If the speaker is stressing the need for better flight school programs while making a speech about airplane accidents, we may assume that pilots are most likely making mistakes. So:
40 percent of all accidents in the last 15 years were caused by pilot error.
We can actually see a connection between the evidences: if pilots are not prepared adequately, then they are more likely to make mistakes that cause 40% of all accidents.