It means that people will know if they are suffering from an illness, meaning that they have the advantage of being able to treat it. A disadvantage could be that if a disease is inactive or uncurable the person would be put through stress for no reason.
The answer that makes the most since is A!
Unemployment was high and working conditions were poor.
B. Crystal size is a function of cooling time. The longer a melt cools the larger the crystals.