throw something in
phrasal verb with throw verb uk/θrəʊ/ us/θroʊ/ threw | thrown
免费添加，额外奉送
If a person or business selling goods throws something in, they provide it for free when you buy something else from them.
When I bought my new glasses, they threw in a free pair of prescription sunglasses. 我买新眼镜时，他们额外免费赠送了一副处方太阳镜。