Question

construction
jack stand construction is simple. usually, the stand is made of steel or aluminum. the base is relatively wide, providing stability.
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 drilled 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 an extra locking pin for added safety.
how is the tubular type jack stand locked?
by means of a steel pin that is inserted into a hole in the tube.
by means of thread and swivel.
by means of a toothed section, that is locked with a cam.
check

Explanation:

The text states that a tubular type jack stand is locked with a steel pin by aligning holes in the stand and the tube and inserting the pin. The other options are not mentioned in relation to the tubular type.

Answer:

By means of a steel pin that is inserted into a hole in the tube.