The advantages to having a civil service system to select government workers is that it eliminates the aspect of it being hereditary. Meaning, you won't automatically get it because of your relation to the previous worker.
The role of a person is the function given to a person or thing in a particular situation. And a role may also be the part played by a person in a particular situation. In our daily lives, we perform different roles in the society, family, and friends.
During World War II, the opportunity cost of dedicating the majority of productive resources to manufacturing weapons and other military goods, was that these resources could not be used for producing other things, not even food or other basics.
At that moment in history, even tough some economies were growing in term of absolut production figures, there was a shortage of food and people suffered from hunger.
You have to measure the temperature of the substance in order to find out. Plus, this only works when the substance isn't in the middle of a reaction