Answer:
In order to answer this question, we need to understand 2 things: <em>which are the principal parts of a verb</em>, and <em>what is the stem of a verb</em>.  
Explanation:
Firstly, there are <u>4 principal parts</u> in latin verbs:
1.	the present, active, first person, singular <em>(Example: </em><em>amo </em><em>– love)
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2.	the present active infinitive <em>(Example: </em><em>amare </em><em>– to love)
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3.	the perfect, active, first person, singular (<em>Example: </em><em>amavi </em><em>– have loved)
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4.	the past participle, singular <em>(Example: </em><em>amatus  </em><em>- loved)
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Secondly, <u>the stem of a verb</u> is the one left once you take away the “–ar”, “-er”, or “–ir” ending.  
Now, we can conclude that <u>the first principal part</u> gives you the present stem of the verb.