Weak entity set is one which does not have any primary key..
(a) is true because weak entity set does not have any existence without strong entity in database. For every entry of weak entity we have corresponding strong entity entry in DB.
let we have employee(strong) and family(weak) as entity sets.
(b)can be false because weak entity set does not have their own primary key so it can have duplication and inconsistency problem that's why it needs strong entity always and hence called as dependent entity.
(c) is obviously true
(d) is true because there is no relationship of tuple partitioning b/w weak and strong entity sets