The Church had great power over people during the Middle Ages because it?

Protected themin times of war
Provided them with education
Decided who could achieve salvation
Controlled food production

Do you have a all of the above ?

I'd say 1 & 2 and a lot of others but I don't see 3 & 4 as historically accurate.

The Church provided some with education, but the general poor were not educated, not given any incentive or opportunities to learn how read or write but were the working masses. Who did they protect in times of War? Themselves. Often the Church was out there, sending people to fight in Wars. Now the salvation answer makes sense - the power the Church exerted in regards to selling salvation, buying souls out of Purgatory, stating who and who was not entering Heaven and/or Hell.

We have to remember that in the Middle ages, often the church and the political power of an area were one and the same, And people were in fear of losing their souls if the church did not give them forgiveness.
There were little if any education and what there was normally were done by the church. And the church controlled great military forces.
And with its vast lands and properties, a lot of the food was grown by share croppers on church property.

But I assume this is a home work question of some sort, and they are looking for the one best answer, so the best answer is read your text book and give your teacher the answer they are looking for.
With that said, often history has many view points depending on what you believe about a subject.
But people would not follow the church normally if they did not want salvation, so the church holds it most power by number 3, The same reason we see extremist religions today control its members

Two and three are definite, but 1 & 4 (especially 1) were often also true.

Yes I know scott, this would be a great debate question, I was hopeing to see JesusHelper and some of the others come here and get a real deep discussion going

But the answer I was looking for, was that it had control because if the people did not do what they said, most often the local rulers would merely kill them.