________ confidence in yourself is the biggest barrier _______ greater progress in your work[ ]

It was in the school ____ he had studied ____ he began the important experiment.

It was so _______this morning that all of cars moved slowly on the road.

It will be hard for us to say goodbye to our dear classmates and teachers before leaving this school ____________ we have so many wonderful memories together.

The key you have just got ____the front door