Among lower-paid workers, union members are less likely than nonunion 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.
(A) imposing stricter limits on medical services and requiring doctors to see more patients, and spend
(B) imposing stricter limits on medical services, requiring doctors to see more patients, and spending
(C) that impose stricter limits on medical services, require doctors to see more patients, and spend
(D) that impose stricter limits on medical services and require doctors to see more patients, spending
(E) that impose stricter limits on medical services, requiring doctors to see more patients and spending
[spoiler]OA:D[/spoiler]

in D:
The second part of the setence is like
'Insurance plans require doctors to see more patients, spending less time with each'
I understand correct answers are correct , but would like to understand the sentence

1. ,+ING modifies the previous clause and the agent is the subject of the previous clause.
,ING can answer 'how Question' for the prevvious clause or can be result of previous clause
2. But It looks like ' Insurance plans is the subject'. Would like to know
Is the agent of ',spending' , Noun: doctors or Insurance plans
3. The sentence looks clear in below format (though it is outside the scope of this topic)
'Insurance plans require that doctors see more patients, spending less time with each'

Can you explain the structure of the D