Question

In which sentence is the word frontier used logically?

Answer 1

Frontier is defined as 1) a line separating two countries, 2) the extreme limit of settled land beyond which lies wilderness, or 3) the extreme limit of understanding or achievement in a particular area.

Right away we can cross out B because the wilderness is pretty close to a frontier. We can also cross out D because it doesn't make sense with the definitions given. So now we are left with A and C.

A is a funny misuse of the word; they probably meant to say "front." So, now we only have C. C is correct, and it makes sense because space does have an extreme limit of understanding in science.