In which sentence is the word frontier used logically? a. the people waiting to see the space show moved to the frontier of the line. b. houses were built on the crowded frontier, well away from the wilderness c. space is the next frontier because most places on earth have been explored. d. the visitors to the space show left their coats and hats in the spacious frontier.

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.