If you are talking about frequency in terms of waves, it is in seconds^-1
Answer:
B) Help produce oxygen
C) Help make foods
D) Help break down dead materials
Explanation:
B - Life on Earth <em>depends</em> on protists since they are the ones who supply us with oxygen.
C - Provide food to other living organisms in food chains/webs.
D - Even, recycle important nutrients just for other life forms to use (some protists may also be decomposers; as they also release nutrients into the environment).
Stable elements are those which have atleast one isotope with no tendency to "decay", i.e., change into anotherelement.
