Answer:
Light does not need a medium to travel travel through, but since waves must have a medium to vibrate, sound is not created where no air is present.
Explanation:
(100, 108)
Due to
1.2x90=108
100, 108
If a red blood cell is 7 x 
m in size, it means that such a cell is 7 microns or micrometer in size. The unit that completes the sentence will, thus, be microns or micrometer.
According to international system of measurement:
m = decimeter
m = centimeter
m = millimeter
m = micrometer or micron
m = nanometer
Thus, a measurement of 7 x m is the same is 7 micons or 7 micrometer.
More on metric conversion can be found here: brainly.com/question/17767575
Water is treated by purifying it by adding slaked lime or potash alum
