Present perfect, past simple and sequencing steps of an experiment

4. Complete the following sentences with the correct form of the verbs in parentheses.

a) I ______ (learn) in this project that electrolytes ______ (save) people's lives.

b) I ______ (not/do) any experiment last school year; but I ______ (do) a few during this one.

c) Scientists ______ (just/make) many discoveries on behalf of human beings.

d) Scientists ______ (just/tell) us how to solve the climate change crisis but people ______ (not/listen) carefully.

e) My science magazine ______ (arrive) almost every week since I first ______ (subscribe).

f) With the help of technology, doctors and nurses ______ (make) significant steps in treating and preventing diseases.

g) The effects of technology on society ______ (be) both positive and negative.

Reading

Individually, put the following steps to perform an experiment in order by writing the correct number on the line.

___ Pour the upper liquid into another container until it separates from the lower liquid.

___ Subsequently, pour the lower liquid into another container to separate it from the sand or earth sediments.

___ Place a container for liquids, preferably transparent, of 500 ml.

___ Add the liquids to the transparent container.

___ Add a tablespoon of sand or soil.

___ Mix the materials perfectly well.

___ Measure 250 ml of water and 100 ml of edible oil.

___ Wait until the elements are separated.