Analysing verb usage

The extract below is from a text which explains how ISOBAR, a portable vaccine-cooling device, works.
The author utilises verbs in a few different ways in this brief passage. Examine the underlined verb phrases, then match the corresponding descriptor to each by highlighting the appropriate text.

Modal verb - used to show present possibility
Passive voice - used to describe a step in a process
Past tense - used to show past reality
Present tense - used to show present reality

Transform the following sentences from active to passive voice (this will transform the text type from instruction to description).

The problem:

In 2015, an estimated 19.4 million children worldwide failed to receive routine immunisation services, with more than 60% of these living in developing countries. Figures suggest that an additional 1.5 million deaths could be avoided if global vaccination systems improve. And, current vaccine programmes in developing countries do not meet the international standards for temperature safe vaccine distribution which leads to vaccines losing potency.

The solution:

ISOBAR works by using a chemical process to provide a long term cooling effect for vaccine delivery.

A mix of Ammonia and Water is heated in a lower pressure vessel. The ammonia vaporises and separates from the water into the upper chamber where it is trapped by a valve. It remains trapped until the cooling effect is needed.

  • First, peel the potatoes and chop them in half.
  • Next, place the chopped potatoes in a large pan of boiling water.
  • Boil the potatoes until they are tender.
  • Drain the pan, then use a potato masher to mash the potatoes.
  • Finally, add butter and cream and mash them into the potato.