请问这句话的意思和句子成分怎么分析,

问题描述:

请问这句话的意思和句子成分怎么分析,
His mother did what she could to send him to a good school
为什么could的后面要 to,这个怎么解释

His mother 是主语,did 谓语,what 引导的句子做宾语从句,to 是宾语补足语.