How do the doppler effect explain why a sirens pitch increases as it approaches you?

Which is best evidence that mary is beginning to change

Ineed on this app i was at ambitious but then all of the sudden i got put back to about 30 points. is there something i can do about this, because i lost all of my progress in this app.

For this assignment, you will create a multimedia presentation in response to the following prompt: research suggests that laughter improves people’s emotional and physical well-being. create a multimedia presentation to inform the audience about the positive effects of laughter on emotional and physical health.