语法和拼写错误检查：塑料瓶回收过程的英文作文修改

检查一下整篇作文的语法和拼写错误，并给出改正后的答案。

本文逐句检查一篇关于塑料瓶回收过程的英文作文，并给出修改后的句子，修改的部分以粗体字显示。

原句： To begin with, plastic bottles is recycled by employees. 修改后： To begin with, plastic bottles are recycled by employees.

原句： Subsequently, plastic bottles are transported to recycling centre. in recycling centre, plastic bottles are sorted in two boxes by staffs. 修改后： Subsequently, plastic bottles are transported to the recycling centre. At the recycling centre, plastic bottles are sorted in two boxes by staff.

原句： In the next stage, the sorted bottles are compressed into blocks.then, these blocks are crushed by certain machines into small pieces which is then washed in tanks. 修改后： In the next stage, the sorted bottles are compressed into blocks. Then, these blocks are crushed by certain machines into small pieces that are then washed in tanks.

原句： in the next stage, washed small pieces are used to produce plastic pellets which is then heated to produce raw material. 修改后： In the next stage, washed small pieces are used to produce plastic pellets that are then heated to produce raw material.

原句： Finally, the raw material is manufactured to produce end products in the last stage of the production process. 修改后： Finally, the raw material is manufactured to produce end products in the last stage of the production process.

请注意，以上修改旨在修正语法和拼写错误。然而，有些修正可能并非唯一正确的答案，具体修正还需根据上下文和意思进行综合判断。