Answer the 4 Qs in two hours. Its simple, I just dont know the topic well enough.

Please answer the four questions below, providing context and examples, as appropriate.

1. How do time-series, panel, and cohort studies differ?
2. What are the main objectives of the literature review?
3. How do stratified and cluster sampling differ? Why would a researcher use these sampling methods instead of simple random sampling?
4. What are the key advantages and challenges when using secondary data?