Question

construction
jack stand construction is simple. usually, the stand is made of steel and sometimes of alum
the base is relatively wide.
the main difference between jack stands is the way in which they are locked. the total service
height is adjustable.
a tubular type jack stand is locked with a steel pin. both the stand and the tube have holes dr
in them. by aligning the holes, the locking pin can be inserted.
the other jack stand has a toothed section which locks using a simple mechanical system. the
mechanical section can only be lowered by operating the steel handle. this type usually has a
额外的锁定销以增加安全性。
which materials are used to make jack stands?
plastic.
steel.
rubber.
aluminum.

Explanation:

The text states that jack stands are usually made of steel and sometimes of aluminum. There is no mention of plastic or rubber.

Answer:

B. Steel, D. Aluminum