<p>When the auxiliary verb of a compound form is <span style="font-style: italic;">essere</span>, the past participle <strong>must agree in gender and number with its subject</strong>. When the subject is feminine singular, you have to change the ending of the past participle to <span style="font-style: italic;">-a</span>. When the subject is masculine plural, you have change it to <span style="font-style: italic;">-i</span>, when feminine plural, you have change it to <span style="font-style: italic;">-e</span>. Examples:</p>
<div class="conjugation_explanation_example_sentence">La pioggia <strong>si è attenuta</strong>. (<span style="font-style: italic;">The rain has let up.</span>)</div>
<div class="conjugation_explanation_example_sentence_note">(The subject is feminine and singular.)</div>
<div class="conjugation_explanation_example_sentence">Gli studenti <strong>sono tornati</strong>. (<span style="font-style: italic;">The students have returned.</span>)</div>
<div class="conjugation_explanation_example_sentence_note">(The subject is masculine and plural.)</div>
<div class="conjugation_explanation_example_sentence">Alcune persone <strong>sono venute</strong> in macchina. (<span style="font-style: italic;">Some people came by car.</span>)</div>
<div class="conjugation_explanation_example_sentence_note">(The subject is feminine and plural.)</div>