Answer :
After items, D.
A colon (:) start an enumeration, which in your case has the items
a microscope,
a test tube,
and a thermometer.
you place the : before the first of the items, so after "items".
A colon (:) start an enumeration, which in your case has the items
a microscope,
a test tube,
and a thermometer.
you place the : before the first of the items, so after "items".