C, that cells cannot be created nor destroyed.
Cells are produce by other cells. Cells can not be man-made nor destroyed.
Explanation:
We know that,
1 mile = 1609.34 m
We need to find how many meters are present in the 12.45 miles. To find it use unitary method as follows :
12.45 mile = 1609.34 × 12.45
12.45 mile=20036.283 meters
or

Hence, this is the required solution.
Those substances which has pH less than 5 are more acidic than Honeybee Venom. Some of them are listed below along with their pH scale,
1) <span>Acid rain and Tomato Juice has a pH of 4.
2) Soda and Orange Juice has a pH of 3.
3) Vinegar and Lemon Juice has pH of 2.
4) Gastric acid has a pH of 1.
5) Battery Acids have pH of zero.</span>
Cs -137 has a half life of about 30 years. If 60 years pass, there is two half lives passed so 1/2 * 1/2= 1/4. Take 1/4 and multiply it with the mass given:
(1/4)*20mg=5mg left