Answer:
Hi! The answer to the first question is A. Nina hears the sound of her drum. This occurs last because all the other events must occur first in order for Nina to hear the drum. She must hit it, the surface of the drum must vibrate, and the sound waves must travel through the air. Only then will she hear the drum.
The answer to the second question is A. Hertz. The number of vibrations per second, or frequency, is measured in hertz (Hz).
Have a great day! - Mani :)
