Which of the following categories of contaminants are by far the most dangerous?
А - Biological
B - Viral
С - Physical
D - Chemical

When a comet collides with earth, it adds material to our planet and causes great damage. therefore, a collision like this is a a. destructive force b. constructive force c. geologic process and event d. constructive and destructive force

Complete each row of the table below by filling in the missing prefix or missing exponent.

Select the correct location on the image identify the element that humans need to breathe. 2015 er r ights reserved