1. observed

2. collected

3. take

4. invented

5. are doing (?)

6. develop

2.1. physicist

2. solution

3. chemistry

4. conservationis

5. measurements

6. exploration

3.1. My computer crashed wile I was downloading a song

2. Tom lost his smartphone when he was running in the park.

3. The first international internet chat took place in February 1989

4. It was so hot yesterday. The temperature rose to 38°

5. What did you do that time last year?

6. I have been waiting for the photos from Sandra last night, but she didn't send me any.

4.1. weren't

2. buy

3. did

4. used to

5. fell

6.Did they use

5.1.C

2.B

3.A

4.B

5.C

6.C

6.1.C

2.A

3.B

4.B

5.A