The correct answer is c) En mi niñez, yo era muy tímida.
The imperfect preterite is the grammatical time in which an action is described in the past; The actions represented at this time do not have a specific beginning or end so that it can present continuity in the action.
The imperfect preterite is generally used with irregular verbs; these verbs are singular since these are modified depending on the grammatical time they are conjugated.
Some of the irregular verbs are "ser","ir" y "estar".
Conjugaciones de los verbos irregulares en tiempo gramatical imperfecto
Pronombre SER IR VER
Tú eras ibas veías
Yo era iba veía
Nosotros éramos íbamos veíamos
Vosotros erais ibais veíais
El/ella era iba veía
Ellos eran iban veían
For example, in this case, in the sentence "En mi niñez, yo era muy tímida." It can be identified that the irregular verb is "era" and is in imperfect grammatical tense; also, the pronoun used is "yo".