Sickly and scarcely are the adverbs in this sentence. I hope this helps :)
The answer is (B) The most crucial safety tip a rider must always follow is wearing a properly fitted helmet.
(A) Informs you on the price of horses
(C) Gives you a definition of what horse reins are.
(D) Describes what a horse looks like.
Sentences that delay the main point until the end of the sentence are called periodic.
