The answer is A .
<span>Rusting of iron. combustion (burning) of wood. metabolism of food in the body. mixing an acid and a base, such as hydrochloric acid (HCl) and sodium hydroxide (NaOH) .</span>
at the top most point if Rupert will not fall then normal force at the top point is almost zero for minimum speed
so here we can say

now if





so above will be the minimum speed
What language is this?? So I can translate it and answer your question
It is round or say spherical to widen the range of photography and it is designed to focus the image as the ray are coming from infinity so !!
I am not an expert of camera but ya it is the main theme !!