Which two of the following were main causes of arab-israeli conflicts in the twentieth century

a. the division of palestine into separate jewish and arab states
b. the ottoman empires entry into world war i
c. egypts nationalization of the suez canal
d. yasser arafat's rise to power in the plo
e. us support for israels military

Two main causes of Arab Israel conflicts in the twentieth century were:

a) the division of Palestine into separate Jewish and Arab states. 

This general statement is quite known, as all three monotheistic religions claim ownership of the Holy Land. 
We can generally say that after the Crusades, Christians remained out of the conflict due to the massive losses they faced when they had tried to invade and conquer it (when Salah Al deen was at power, before the rise of the Ottoman empire). 

I am not sure about this one, but I assume the best answer would be D)US support for Israels military

It's a generally known fact that the US is a close ally of Israel, and this is mainly why there are immense issues and conflicts between the two religions whom are living in the same territory/land. 

Generally, this topic tends to be those ones that kind of get biased responses (you know, due to people taking sides). I tried making this response as non-biased as possible, filtering it from opinion and such. 

Hope this helps. Comment if you need assistance. Glad to assist! :)