While Padmi looks frantically for her pen, her sister calmly writes with it. "While Padmi looks frantically for her pen," cannot stand alone. Using it in "While Padmi looks frantically for her pen, her sister calmly writes with it." makes it dependent on the second part of the sentence.
B.
Read this line, out loud.
It was a short pause that contributed to the flow of things. This applies even in a sentence.
