2. In research aiming to investigate the clinical characteristics of familial aggregation of hypertension, a female patient with hypertension is selected as a hypertensive proband and hypertension information about her family members. Let A1 = “her sister has hypertension,” A2 = “her brother has hypertension,” A3 = “her daughter has hypertension,” and A4 = “her son has hypertension.”

Answer the following questions:

(a) What does A1 ∪ A2 mean?

(b) What does A1 ∩ A2 mean?

(c) What is the relationship between A1 ∩ A2 and A1 ∪ A2 ?

(d) What does A1 ∪ A2 ∪ A3 ∪ A4 mean?