Please help classify the following as a. discrete/continuous, b. level of measurement (interval, ratio, nominal, ordinal and briefly why your answer is so. Please include any statistics reference (optional). Thank you!

1. Measurements of the time it took you to get 2 doses of Pfizer vaccine

2. The numbers of calendar years (such as 2020, 2021, 2022, etc.)

3. The numbers of dairy cows on different farms

4. Nationality of a survey's respondents

5. Number of active COVID-19 cases in Singapore