"These books are heavy."

Translation: Buku-buku ini berat.

[dgaeremie]

Buku ini berat

[Away54]

Is it inconsistent? In another lesson, Duolingo says, "These trousers are ..." but accepts only "Celana ini ..." and rejects "Celana-celana ini ..." or "Celana-celana panjang ini ...".

Here, the opposite, "Buku ini ..." is rejected.

[Appers6]

Why does this answer insist on buku-buku? Surely "buku ini" can mean "this book" and also "these books"?

[Away54]

When we want to lift a lot of heavy things and feel tired, we say, "Barang-barang ini berat". The word " barang-barang" itself implies a lot of "barang". It's similar to "buku-buku".

[RainyKucing]

"Buku ini berat" was marked incorrect. Time to get kicked out of my lesson