To conjugate -ir verbs, such as vivir, first you should . add the verb endings -o, -es, -e, -imos, -ís, or -en to the stem then take out the stem viv.

add the verb endings -o, -es, -e, -imos, -ís, or -en to the entire word.

leave the stem vi, and then add the verb endings -vor, -ves, ve, -vimos, or -ven to the stem.

leave the stem viv, and then add the verb endings -o, -es, -e, -imos, -ís, or -en to the stem.

The last choice:

Leave the stem viv, and then add the verb endings -o, -es, -e, -imos, -ís, or -en to the stem.

Explanation:

When conjugating regular Spanish verbs (in this case present tense), the only part of the infinitive (meaning any Spanish verb word ending with an -ar, -er, or -ir) you want to take out would be the -ar, -er, or -ir endings. The rest of the word, or the stem, would be left alone. Therefore, the last choice would be correct.