1. A beaver tail is a big,flat bread.

Question

2. A beaver tail is big, flat bread.
3. Beaver tails are big, flat bread.
4. Beaver tails are a big, flat bread.
5. Beaver tails are big, flat breads.
6. Beaver tails are big and flat.
7. beaver tails are big, flat.

(Which expressions are grammatical?)

Answer 1

1. A beaver tail is a big,flat bread. no
2. A beaver tail is big, flat bread. no
3. Beaver tails are big, flat bread. no
4. Beaver tails are a big, flat bread. no
5. Beaver tails are big, flat breads. no
6. Beaver tails are big and flat. yes
7. beaver tails are big, flat. no

You could make 1-5 correct by writing the sentence like this:

Beaver tails are like big, flat pieces of bread.