what is the best explanation of how scientists know cyanobacteria existed 3.5 billion years ago

A; They were found in fossils that scientists were able to date

B; They have learned alot

C; None Of These

D; They saw it growing today and were able to date it back

If these are the missing choices: a. to determine skin temperature, place the back of your hand against the patient's skin.b. determine body temperature by touching the patient's hands and feet.c. skin temperature will tell you very little about this patient's condition or well-being.d. the patient's skin temperature and color will likely be warm and red.my answer is: a. to determine skin temperature, place the back of your hand against the patient's skin. using the back of the hand to check for temperature rather than the palm is more effective because the back of the hand has more nerves that can feel and transmit the temperature than the palm.