Among lower-paid workers, union members are less likely than non union members to be enrolled in lower-end insurance plans imposing stricter limits on medical services and requiring doctors to see more patients, and spend less time with each.
Option Elimination -
(A) imposing stricter limits on medical services and requiring doctors to see more patients, and spend - ING modifier without comma modifies the immediate noun. So, imposing modifies "plans." But then "and" demands parallelism. Before and we have a clause, and after and is a phrase. Also, the intended meaning is that "plans" impose stricter restrictions and require doctors to see more patients (list of 2 items with parallel structure - clauses on both sides - plans impose and plans require), and as a result of requiring to see more patients they spend less time with each. So, the ideal structure is "plans impose ...and restrict, spending less ...."
(B) imposing stricter limits on medical services , requiring doctors to see more patients, and spending - wrong parallelism.
(C) that impose stricter limits on medical services, require doctors to see more patients, and spend-trap parallelism as if all three items are parallel. "plans impose....plans require ....and plans spend less time with each. Ridiculous meaning. Meaning understanding is key to eliminating this option.
(D) that impose stricter limits on medical services and require doctors to see more patients, spending - ok
(E) that impose stricter limits on medical services, requiring doctors to see more patients and spending - wrong use of ING modifiers. "requiring" and "spending" modify "plans impose," conveying plans impose a restriction, and as a result, plans require doctors to see more patients and plans spend more time with the patients. Ridiculous meaning.