Which is the best label for the dotted-line arrow?

Which of the following areas have the highest population density? a) quebecb) united statesc) californiad) new york city

How would i answer this for an exam?

[ou.01]which of these is the most likely use of an electromagnetic wave which has wavelength shorter than microwaves but longer than visible light? o heat food safely o neat food safely o take images of bones and teeth o transmit radio and cellular phone signals o take images of bones and teeth o transmit radio and cellular phone signals o detect the location of objects which emit heat