The mixture of his improved self-confidence and never-ending efforts is ________ lies behind his rapid progress in his study.

下列各句中，加点的成语使用正确的一项是（ ）

The students in Class 3 planned to sell old books to _______ money to help the new student.

The old couple often take a walk after supper in the park with their pet dog them.

I want to show you is my gratitude andrespect for your continuous and selfless help