Re: Adverb or Adjective?
In the first, "fast" describes how the train was MOVING. Moving is a verb, so you use an adverb to describe it.
In the second, "tired" describes SARAH. Sarah is a person, a noun. Adjectives describe nouns.
There are some verbs (is, feels, smells, looks, seems) that describe the thing/person, so you use an adjective.
I feel good.
It smells delicous.
You look beautiful
She seems tired.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.