The two orders use different agreement in the rule taught here.
دَخَلَ الْمُعَلِّمُونَ
The verb comes before an explicit plural subject, so the verb is singular.
الْمُعَلِّمُونَ دَخَلُوا
The plural noun comes first as mubtada, so the following verb is also masculine plural.
Therefore الْمُعَلِّمُونَ دَخَلَ is not the required conversion. The verb must show the number and gender of the preceding mubtada.
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Changing a Verbal Sentence into a Nominal Sentence
The two orders use different agreement in the rule taught here.
دَخَلَ الْمُعَلِّمُونَ
The verb comes before an explicit plural subject, so the verb is singular.
الْمُعَلِّمُونَ دَخَلُوا
The plural noun comes first as mubtada, so the following verb is also masculine plural.
Therefore الْمُعَلِّمُونَ دَخَلَ is not the required conversion. The verb must show the number and gender of the preceding mubtada.