No one knows how the huge rocks _______ and _______ without our modern machines eight hundred years ago.

_____ on computers for storing information that people are unable to remember basic things.

We must act now because time is _______.—Yes. Let’s start.A．coming out

With the development of the intelligent robot technology, people _______ the importance of cooperating among robots, and the challenge in practice.

_________the mistakes in red ink is one of the ways that teachers usually use to remind students to pay attention to their work.