选词填空。 a an 1.--What's this? --It's ______apple. 2.--What' this? --It's______red apple. 3. It's______big egg for you. 4. Look, that is______English book. 5.--Lily, I'll give you______orange coat. --Thank you. But I like______ blue coat very much. 6. It's______umbrella under the tree.