Hello, I am a Spanish speaker so let me help you. In this exercise, we need to conjugate the verb conocer correctly. Let me explain, in Spanish, the simple present tense (el presente or el presente de indicativo) is used to talk about habitual actions, routines, things happening now or in the near future, universal truths, facts, hypotheticals, lapses of time, and for ordering in restaurants and stores.
There are both regular and irregular indicative forms. In this problem we need to know the regular form. So, you can recognize some endings for regular verbs, one for ar verbs, one for er verbs and one for ir verbs. The verb conocer ends in er, therefore, remove the infinitive ending er and add the ending that matches the subject. Accordingly, the right answer is d. conocen:
Ellas conocen a los profesores de español (They know the Spanish teachers)