stone age people protected their families by____fire to drive off wild animals at night.A.usedB.usingC.usesD.used to

stone age people protected their families by____fire to drive off wild animals at night.A.usedB.usingC.usesD.used to
stone age people protected their families by____fire to drive off wild animals at night.
A.usedB.usingC.usesD.used to

stone age people protected their families by____fire to drive off wild animals at night.A.usedB.usingC.usesD.used to
B using.
by是介词后面接动名词.
石器时代,人们通过用火在晚上驱赶野生动物来保护他们的家人.

3B using

using
by+doing sth.

using,