To answer the question, "How do students in the United States pay for their higher education?" a questionnaire was sent out to collect responses from students at higher education institutions in the United States. Categorize the following method of sample collection:

Creating an email list of every student enrolled in higher education in the United States and sending the questionnaire to every 10th email address.

• 1. ) Simple random sample
• 2.) Systematic sample
• 3.) Convenience sample
• 4.) Stratified sample