Ask them to place a thermometer in the centre of each container and record the temperatures at 2-minute intervals over a 20-minute period.
(them; to place; a thermometer; in the centre of each container) (them; to record; the temperatures at 2-minute intervals over a 20-minute period)
them them
to place to record
a thermometer in the centre of each container
the temperatures at 2-minute intervals over a 20-minute period