“Three distinct points in space always determine exactly on unique_______.”

Of the following words, write in the answer box the ones that, when placed in the blank in the statement above, would make the statement true: line, circle, square, triangle, plane.”

Is the answer a triangle because it says a three distinct points in space. I know that it can't be a circle because it doesn't make a circle, square is not the answer because, it needs four distinct points, and I don't know for sure what is a plane. Line can be a straight line and a crooked line, right?

Please help me on this problem. Thanks!