Without the friction (摩擦力) between feet and the ground, people would ______ be able to walk.
— What do you think of the novel written by the well-known writer? — Sorry, no _________!
If my father ______ here yesterday, he would have stopped me from going surfing.
In my opinion, we need to begin ______ we stopped yesterday to ensure we won’t miss anything.
Steve Jobs’ success in digital field proved ______ it took to be a best CEO.
The equipment for disabled people should be ______ easy reach in public places.