Why is jonathan so happy that his family has "five heads" on their shoulders?
a. millions of people died during the nigerian civil war
b. igbo mythology warns of a curse that causes deformed babies
c. his wife just had a baby, which added to the family of four
d. "heads" refers to bags of british pounds, and five bags is a small fortune

I believe the answer is: a. millions of people died during the Nigerian civil war

The implication that we can take from the sentence is that it is very common for People during the civil war to constantly lose their members of family in the war.

So, when jonathan say he is happy his family has five heads, he meant that even if one or two of his family died, there would be someone that alive to take care of the family.

onto a large boat, and mark the water level that the boat sinks to. then, take the elephant out and put a bunch of marked weights onto the boat until it reaches the same water level. add up the masses of the weights to get the weight of the elephant.