Regarding trading and volatility, select the most suitable answer below $($single choice$).$

Question $4$Answera.Trading does not cause volatility.

b$.$Volatility does not cause trading.$$

c$.$Volatility and trading are synonyms, just two different words to describe the same phenomenon.

d$.$Volatility seems to be at least partially caused by trading, as volatility it is much lower over non$-$working days, even for variables that depend on the weather.