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Grammar

Past Simple is used to speak about simple actions, facts in the past.

To form Past Simple we use:

- verb (V) + ed forregular verbs, ex. invite – invited/ visit – visited

- V₂ (Past Simple form) for irregular verbs, ex. go – went/ come – came

(see Irregular Verbs)

For negative and interrogative we use did + V;

Ex., We did not go to the cinema yesterday, we had a test.

When did you meet him?

1. Put the verbs in the correct form Past Simple.

History of Community Water Fluoridation

The history of community water fluoridation in the USA may be categorized into four separate periods: 1) clinical discovery phase, 2) epidemiologic phase, 3) demonstration phase, 4) technology transfer phase.

The first period a) _____ (last) from 1901 to 1933. During that period dentists b) _____ (determine) the cause of developmental enamel defects present in people. In 1901 Dr.Frederick McKay, who c) _____ (be) a recent dental school graduate, d) _____ (move) west and e) _____ (set) up a dental practice in Colorado Springs. He f) _____ (notice) that some of his patients g) _____ (present) with discolored enamel. This sometimes h) _____ (exhibit) surfaces that i) _____ (be) rough, uneven or pitted. This enamel condition j) ______ (not/ occur) among individuals who had not lived in that area as young children. McKay k) _____ (name) this condition “mottled enamel”.

2. Make the sentences negative; put questions.

1) Dentists examined children in various nearby community. (Did)

2) McKay published very important findings in “Dental Cosmos”. (What)

3) People with enamel fluorosis experienced less dental decay. (Why)

4) In the early 1930s H.V.Churchill, a chemist with Aluminum Company of America, used a new method to examine the water. (Did)

5) H.V.Churchill identified high levels of naturally occurring fluoride in the drinking water supply. (What)

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