Question

why should a circular saw that does not have an upper blade guard never be used?
the exposed blade poses a danger.
the trigger lock will not work properly.
the safety features will be disabled.

Explanation:

The upper blade guard protects users from the spinning blade. Without it, the blade is exposed and can cause serious injury. The other options are not related to the absence of the upper - blade guard.

Answer:

The exposed blade poses a danger.