Normal books will do, as long as they are not evil novels or anti-country, anti-society or even anti-humanity. Although the investigation will still be quite strict, it doesn't matter as long as it's not illegal. So don't worry too much. The government is also reasonable. We will never wrong good people for no reason, and we will never let bad people go easily. As long as you keep walking, why worry? My suggestion is that as long as it is legal, it doesn't matter, just take it back to China.