Add the apostrophes in the correct places. then choose the correct answer /, a or b​

Question

Add the apostrophes in the correct places. then choose the correct answer /, a or b​

Answer 1

1a. My mother’s new husband is my stepfather.

2a. My sister’s husband is my brother-in-law.

3b. My son’s wife is my daughter-in-law.

4b. My father’s wife’s daughter is my stepsister.