Source: Kaplan

Handwriting analysis has recently been boosted by the invention of 3D micro-profilometry, which can be used
to calculate the pressure used at a crossover point such as the center of a figure eight, and
to detect the starting and ending points of strokes not detectable via conventional 2D analysis.

(A) the starting and ending points of strokes
(B) the locations of starting and ending points of strokes that are
(C) where starting and ending points are located, which are
(D) where starting and ending points are located
(E) where the starting and ending points are located, which are

Use of Where is absolutely meaningless since there is no location here and is also not parallel otherwise.
C, D and E can be eliminated.

(C), (D), and (E) all use the non-parallel "to calculate the pressure . . . and to detect where X and Y are located". Parallel structure would be either "to calculate the pressure . . . and to detect X and Y" or "to calculate how much pressure . . . and to detect where X and Y . . ."

(A) the starting and ending points of strokes
(B) the locations of starting and ending points of strokes that are
[spoiler]
I felt the verb are is required to connect the strokes to not detectable phrase and selected B.
Please explain why B is wrong and A is correct with no such verb.[/spoiler]