Correct Option: B
According to question,
Samant remembers that his brother's birthday is after 16th but before 20th of January
it means birthday will be on of any one date
17th, 18th, 19th January.
According to his sister remembers that her brother's birthday is after 17th but before 19th of January.
it means birthday will be on
Her brother's birth day is on 18th of January as 18th January is common to both the groups of dates.