been living in the United States fortwenty years,but seldom _______ so lonely as now

It’s not what you say but what you do that _______.

He is very firm about it; I cannnot _____ him

The companies are working together to create ________ they hope will be the best means of transport in the 21st century.

continue with the training，Sir—Sorry, you can’t you haven’t recovered from the knee injury．