Answer:
b. Veteran trainers offer a great deal of love and discipline to <u>whatever dogs they train.</u>
Explanation:
The noun clause "whatever dogs they train" is the object of the preposition to.
a. These experts say that the best time to begin a dog’s training is <u>when the dog is still a puppy</u>.
This is a noun clause that functions as a <em>predicate nominative</em>.
c. These experts say <u>that the best time to begin a dog’s training</u> is when the dog is still a puppy.
This is a noun clause that functions as a <em>direct object</em>.
d. <u>Whoever trains a dog</u> should have experience.
This is a noun clause that functions as a <em>subject</em>.