Question

to be efficient and keep down costs, engineers want to use the smallest amount of explosive possible. to figure out how much they need, engineers study the building plans and also do tests. they pick a column that isnt holding the building up, drill a hole in it, fill it with what they think is the right amount of explosive, and set it off. if the column doesnt break, they need a bit more explosive. if it shatters completely, they need a bit less. once the demolition experts know how much explosive to use, they drill small holes in other columns and put the explosive inside. steel columns are stronger than other types of columns. they need a different kind of explosive, called a shaped charge. when these go off, they make a very narrow blast that can slice through steel like a knife. for concrete columns, dynamite often does the trick. to keep pieces of concrete from flying out during the explosion, the columns are wrapped in wire mesh and a special strong fabric. why do experts use one kind of explosive for steel columns and another for concrete columns? steel is sharper than concrete, so it requires much more explosive. experts have to blow up steel columns but use a special strong fabric to break apart concrete columns. steel is stronger than concrete, so it requires a more powerful explosive. experts must put explosives in holes for steel columns but wrap explosives in mesh for concrete columns.

Explanation:

The text states that steel columns are stronger than other types of columns, so they require a different and more powerful explosive (shaped - charge) compared to concrete columns for which dynamite often suffices.

Answer:

Steel is stronger than concrete, so it requires a more powerful explosive.