suitable sampling technique

a) Identify suitable sampling technique for the situations below. Mr David selects all students sitting at group 2 and group 5 in his classroom as sample. ii) Mr David chooses 5 girls and 7 boys from his class. iii) Mr David samples his class by selecting every fourth students on his class list. iv) Mr David picks 10 numbers from his clutch and each number is assigned to a student. (4 mark)