they settled near sources of food, and those areas that produced more food became more polulated.

those area that에서의 that은 주격 관계대명사죠???
그리고 became more populated에서 왜 p.p를 쓴 거죠 ??
수동태를 만들기 위함인가요 ??
그럼 became대신에 be동사인 were 써주면 안되나요 ????
정확하고 친절한 답변 부탁드립니다 .^^