If there is mandatory participation between 2 entities in an ERD, does this mean neither of them are strong entities?

Say I have entity A with primary key "key_A" and entity B with primary key "key_B”. I also have that key_A is a foreign key in entity B. My business rules state that every instance of A is related to at least 1 instance of B, and every instance of B is related to exactly 1 instance of A. In a situation like this, how would you classify A and B as weak/strong entities?