a/an + 文具名词 — 英语阅读题

阅读短文，回答问题。 It is Sunday. Lily puts her school things in her bag. She has a pencil, a ruler and a pen. Her brother Tom has an eraser and an English book. Tom also has a pencil box. Lily looks at Tom's things and says, "Tom, you have two things with 'an'. I have three things with 'a'." Then they put everything into the bag and go to school the next day. Question: How many school things do Lily and Tom have together (一共)? Please list all the school things in the short passage (请列出短文中出现的所有文具).