If students have given sufficient time and attention to their work, they should have increased considerably their command of English change to passive voice

The above sentence changes to a passive voice, thus:

"Their command of English should have increased considerably if sufficient time and attention were given by students to their work."

The passive voice always follows this pattern: Object + Verb + By Phrase.

When the emphasis is not on the doer but the object of the action, the passive voice is used.

In the above sentence, the passive voice emphasized "their command of English" and "sufficient time and attention," which are objects of the sentence.

Students, who are the doers of the actions, were relegated to the background because the emphasis is not on the doers but the objects of the action.

Thus, the passive voice is always used when the object must be emphasized.

Learn more about the usage of the passive voice here:

theres no poem plesae include that

im not sure about this one