________its low cost, the appeal of iron as a building material lies in its strength, its resistance to fire, and its potential to span long distances

It was not until the 18th century that manrealized that the whole of the brain was involved in the working of the mind，

He ________ get into his own house because he has lost his keys.

_________ to the association of success with money that the thought of giving up good salary for an idea seems like a little bit crazy.

American students take part in a wide variety ofafter-school activities _______ they develop their social skills.