$$\text{A}$$. Throw a coin randomly. It has a $$50\textbackslash\%$$ chance of landing head up and a $$50\textbackslash\%$$ chance of landing tail up.  $$\text{B}$$. Throw a die, and number of the dot shown may be any number from $$1$$ to $$6$$.  $$\text{C}$$. Sun sets in the west.  $$\text{D}$$. It may not rain in cloudy days.  So $$\text{C}$$ is the answer. 
In the following events, the certain event is~\uline{~~~~~~~~~~}~. 
1. Toss two identical coins and both land on heads. 
2. Throw a fair die and number of the dot shown is $$3$$. 
3. Sun sets in the west. 
4. It must rain in cloudy days. 