The correct anwser would be climate, because the great potato famine is part of the climate, and was a deciding factor as to why they should leave. I hope you find this helpful, and good luck! :P
I think its A but I'm not positive about this one.
The answer is B. In South Asia, Islam found a place in a long-established civilization as invasions by Turkic-speaking warrior groups from Central Asia, recently converted to Islam, brought the faith to northern India. Thus the Turks became the third major carrier of Islam, after the Arabs and Persians, as their conquests initiated an enduring encounter between Islam and a Hindu-based Indian civilization.