To make members of a team perform better, the trainer first of all has to know their and weaknesses.
The rich ____ not always happy.
I, who____ your friend, will try my best to help you with your English.
The United States of America _____one of the most developed countries in the world.
The whole class _____the teacher attentively.
Jane is one of the best students in her class who _____by their teacher.