What isotope pair used to determine the age of fossils

Carbon 14 and Potassium -40

Explanation:

Radioactive isotope of carbon -14 is used in carbon dating. The half-life of C-14 isotope is 5730 years. It is an efficient isotope which can be used to determine the age of fossil which are younger than 75 thousand year old. Isotopes of other element are also used for dating such as Potassium -40 (half life = 1.25 billion years).

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

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b tumor cells have a cell wall instead of a membrane

explanation:

tumor cells different from normal cells because tumor cells have a cell wall instead of a membrane.