Question

What is the subject, direct object, indirect object, and object of the preposition in this sentence?

That Leo Tolstoy is revered today is a testament to his genius.

Answer 1

Subject: That Leo Tolstoy is revered today
There's no direct object or indirect object
Object of the preposition: genius

Explanation:

The subject of the sentence is called a noun clause. It is a clause because it has its own subject and verb.

It is also a dependent clause which cannot stand on its own because of the word that (a relative pronoun) at the beginning of the clause.

A noun clause functions as a regular noun in a sentence.

Here are examples of different functions of a noun in a sentence:

Noun as subject of the sentence:

He is patient.
That he can endure everything is love.

Noun as direct object of the sentence:

She ate spaghetti .
He ate whatever she offered to him .

Noun as subject complement:

I am Carmen .
I am a girl .
I am what you see .

Noun as object of the preposition:

He throws the ball at the fountain.
The child throws the ball at what his father is building.

You asked to identify the direct object and indirect object, but there can't be these two types of object in the given sentence because * is * is an intransitive linking verb. Only transitive verbs can take objects.

Examples of sentences with transitive verb:

The ball hits him.

verb : hit
subject : who/what hits? the ball
direct object : the ball hits who/what? him

He throws the ball to Ronnie.

verb : throws
subject : who/what throws? He
direct object : He throws who/what? ball
indirect object : He throws ball to whom? Ronnie

Examples of sentences with intransitive verb:

1. The watch fell.
2. I cried last night.

Noticed something?

1. verb : fell
   subject : who/what fell? the watch
   direct object : the watch fell who/what? There's none.

2. verb : cried
   subject : who/what cried? I
   direct object : I cried who/what? There's none.
   adverb : I cried when? last night

I hope this helps. :)