A. Superlatives form is ‘-est’ or most: the rules are the same as those for the comparatives
A1. good -> best, bad -> worst, far -> furthest/ farthest
B. normally use ‘the’ before a superlatives (the most famous etc.)
C. The superlative of old is oldest. Use eldest (or oldest) when we are talking about people in a family.
D. After superlatives we normally use in with places
D1. also use ‘in’ for organisations and groups of people
D2. For a period time, we normally use ‘of’
D3. often use the present perfect (I have done) after a superlative.