Many rules in English are ______, and large numbers of students feel ______ them.

I’ve asked several people what happened, but no one will give me a          answer.

A group of children are looking into the box, ____ about what can be inside.

Calculations，which are astronomically exact，have been made ________ with the use of computers.

—Are you satisfied with her answer? — Not at all. It couldn’t have been _____.