The right answer is D (less responsive to antigens)
It is proven that, after puberty, thymus activity (an organ that is included in the lymphatic system, producing T cells that pick up antigens) decreases and that in adult and aged people the thymus has no role. Work done in humans indicate that in fact the cellularity begins to decline from birth in favor of lymphocyte perivascular spaces and connective and adipose tissue, which leads to a decrease in the capture of antigens.
It will become a theory after repeated experimentation
The three types of chemical bonds are Ionic, Covalent, and Metallic
Answer: Option (C)
Explanation: The rocks at the continental crust are present since a long time, and the oldest rocks so far encountered from the continental crust is approximately 4.4 billion years old.
This has been determined by the Uranium-Lead dating method (Ur₂₃₈-Pb₂₀₆).
Oceanic rocks are estimated to be of very recent age i.e about only 180 million years old.
Answer:
This is a physical change.
Explanation:
A change in state, such as a change from solid to a liquid, is a physical change.