Tell the students a story that will probably make them curious about the topic. For example, '' Last night I saw a very big , bright and strange light in the sky. What may it be? ''

Give the tapescript of the previous listening activity to the students. Ask the students underline all modal verbs in the script. Guide the students to work out the rules themselves. Ask the questions : '' Which modal means that there was a possibility? , Which modal means that there is a possibility?,Which modal means that the speaker is sure of something? , Which modals refer to past/present? , How does the verb form change in both cases? ''etc. While students answer the questions, collect the modals on the board in an organized way. Focus on the form and meaning. Do the concept checking Drill the past and present forms in isolation and in context.

Give the instructions. Students rewrite the sentences with the modal verbs in brackets to add speculation individually. They check in pairs. Run the feedback. Clarify any necessary points. Give the instructions for the activity 2 Students complete the blanks with can't, must or might. They check in pairs. Run the feedback. Clarify any necessary points.

Tell the students that they are going to read about some strange mysteries which have never been explained and that they are going to speculate about possible explanations. Ask the students to work in groups of five. Give one copy of mysteries to each student from the copy of Worksheet 19b (mysteries) Explain that each section contains a different unsolved mystery. Ask the students to take it in turns to read out their unsolved mystery to the rest of the group. Tell the students that the whole group should suggest two or three possible explanations for each mystery. Tell the students that each student should write down the group's suggested explanations on the back of their section of the worksheet. While they are doing the task, monitor them. When they finish it, compare the results with the groups. After comparing, give each group a copy of Worksheet 19c (possible explanations) Tell the students that they are going to read some ways in which people have tried to explain the mysteries they have read about but the explanations are not in the correct order. Tell the students that their task is to match three possible explanations to each mystery. While they are doing the task, monitor them and note down some most common errors for the further error correction part. Check their answers to see if they had the same ideas.

Board some sentences with errors of the TL that the students have produced. Ask the students work in pairs and correct them explaining why the sentence was wrong.