thu song o ba moi truong; bay, nuoc va can

thu kiem an vao chieu hoac dem thuc an la tu dong vat

thu tinh trong thai phat trien trong tu cung cua me

co hien tuong thai sinh

ban le an noi sai roi bo thu tui lam gi co thu mo vit

ban oi do lai vo on lai tu dau dai to muon giai lam nhung dai qua

de phan biet giua cac lop ta can biet ve doi song va cau tao trong , ngoai

bo nao chim bo cau phat trien la co nao truoc va tieu nao phat trien