To improve her understanding of the common sense of bicycling: bicycling for ladies, lorena wrote this paraphrase of a sentence.

knowing when to lighten up on the top pedal requires practice.

which sentence is being paraphrased?

to learn to balance, have the saddle raised as high as possible, so that the ball of the foot just touches the pedal at its lowest.
the beginner usually exerts too much pressure on the pedals, and has to correct the falling tendency of the machine.
to take the pressure off the ascending pedal at the right moment is a more difficult matter.
when the pedal is at the highest point, the toe should be raised and the heel lowered.

The sentence being paraphrased is option C) "To take the pressure off the ascending pedal at the right moment is a more difficult matter."

There are several hints that help us identify the paraphrased sentence since there are phrases with similar meanings:

To take pressure off: to lighten up. These two phrases imply the meaning of "slowing down the movement"

Ascending pedal: top pedal. Both words are synonyms

More difficult matter: requires practice. These phrases refer to the difficulty of the action.

in the section of speech is not

the correct answer is 4) infinitive phrase with a direct object

the explanation is that the infinitive phrase, "to with the younger children", functions as the object. it means the thing that the subject does.

1) no infinitive is incorrect because there is an infinitive verb in the sentence.

2) an infinitive only is incorrect because it is not in isollation. it is part of an infinitive phrase.

3) infinitive phrase with a subject is incorrect because in this example the infinitive phrase does not function as the subject doing the action of the sentence.