Answer:
The answer is B. might.
Step-by-step explanation:
First, let`s identify which conditional this is, so we`ll have to name the verb parts of these clauses:
If you lead by example - verb is lead and it is present simple tense.
your sister might even stay in school - might stay - it a modal construction that consists of a modal verb might and bare infinitive of a verb to stay
This combination is seen in the second conditional. Modals can be: would, might, can, may...
Answer A - example does not affect the sentence in any way.
Answers C and D - stay and lead - those are the verbs that have to be in these clauses. So what is needed so that this can be a conditional sentence is modal verb might.