This sentence describes an activity that is happening at the exact moment the speaker is talking.

This sentence describes an activitity that is in progress, but not happening at the exact moment the speaker is talking.

This sentence describes a changing situation.

This sentence describes an activity that is happening at the exact moment the speaker is talking.

This sentence describes an activitity that is in progress, but not happening at the exact moment the speaker is talking.

This sentence describes a changing situation.

This sentence describes an activity that is happening at the exact moment the speaker is talking.

This sentence describes an activitity that is in progress, but not happening at the exact moment the speaker is talking.

This sentence describes a changing situation.