Disadvantages of asexual reproduction include: offspring compete for food and space, extreme temperatures can wipe out entire colonies, negative mutations can destroy many offspring.
The element starts off as 100%. half of 100% is 50% and half of 50% is 25%. the element has emitted 2 times the half life which is 10,000 x 2 = 20,000
the fossil bone is 20,000 years old
I believe the answer to your question is c
