Hydroxyapatite is the major component of bone that contributes to its hardness.
I think the correct answer from the choices listed above is option A. The anatomical adaptation which helps an elephant regulate its body temperature are its large ears increase surface area so that more heat is lost by radiation. Heat can be released as they flap these ears. So there is your correct answer
There are so many examples for that in different areas, like biology experiment carried out in our lab recently.
Here's one link:https://www.creative-biogene.com/support/Knockout-Cell-Lines-in-Antibody-Screening-and-Validation.html
The best example that illustrates a sensitive period is
letter b, where the child tries to learn in speaking a second language because
this is considered to be a sensitive period in which is the period for a
development of new opportunities that a child could learn in which learning to
speak a second language is considered to be a sensitive period.
The correct answer is neuroplasticity.
Neuroplasticity or brain plasticity is the property of the brain to change. Neuroplasticity can be observed at different levels. For example, changes at the cell level can affect connections between neurons (synaptic plasticity), while non-synaptic plasticity refers to changes in the intrinsic part of the neuron. On the other hand, larger-scale changes are usually made by environmental stimuli. Emotions may cause neuroplastic change through activity-dependent plasticity, which is significant for the recovery from brain damage.