ANSWER:- option A formation of fossil fuels.
Explanation:-
So, the formation of fossil fuels is the phenomena which takes the longest time in the carbon cycle.
Formation of fossil fuels is a process in the carbon cycle that takes the longest time to complete.
How much time taken by fossil fuel formation?Fossils are the remains of organisms that died more than 10,000 years ago so this means that 10,000 years are required for the formation of fossil fuel.
So we can conclude that formation of fossil fuels is a process in the carbon cycle that takes the longest time to complete.
Learn more about carbon cycle here: https://brainly.com/question/1194643
Gene therapy is a way doctors can treat a disease by inserting a healthy gene into a patient's cells, instead of using drugs or surgery. The new version of the gene helps the patient's body fight the disease. Gene therapy is A) considered a very safe technique. B) still being researched and is not used on humans. C) still being tested and is used for diseases that have no cure. D) used frequently today to prevent many common childhood diseases.
The answer is; C
Gene therapy is still not considered safe and has not been approved for humans, especially due to errors in inserting of DNA at the target site and also random relapse of the DNA from its inserted site. Gene therapy, however, can be sanctioned when its benefits outweigh its risks such as in terminally ill patients - with the approval of the patient and local relevant policies/authorities. Gene therapy, today, is being tested with innovative tools called CRISPR/Cas9.
Answer: C) still being tested and is used for diseases that have no cure.
Explanation: It is considered as risky and is only used for diseases with no cures. It's not used for those diseases with many cures and it is not safe.