Unit 2  In the lab
1.First of all, don't come in here without a teacher.That's not allowed. Once you are here, listen to the teacher. Follow the teacher's instructions.
2.Don't touch anything unless your teacher tells you to .= Don't touch anything if your teacher doesn't tell you to .
3.Paul will never forget his first chemistry teacher. He was a little man with thick glasses, but he had a strange way of making his classes lively and interesting. And his lessons were not easily forgotten.
4.The bottle was filled with  petrol. =  The  bottle was full of petrol.
5. As the students watched him quietly, he mixed the three bottles together.
6. It was Paul's first important lesson as a student of chemistry and he never forgot it.
7. At the beginning of class, the students say hello to the teacher, and at the end of the class, the teacher says goodbye to the students.
8.  You can never be careful enough. =   You can't be too careful.
     
     Paul never forgets his first teacher of chemistry . The teacher was a short man with a pair of thick glasses. He always made his lessons lively and interesting.
      One day in a chemistry experiment in the lab, he made a mixture by filling a cup with some petrol, castor oil and vinegar. The students looked very interested and listened quietly. The little man then said to the students, "Now, watch me carefully. " He dipped one finger into the cup for a few seconds, took it out and  put his finger into his mouth. He looked rather pleased and said with a smile, "It tastes delicious. "
       He then asked the students to do just what he had done. He handed the cup around the class. Each  student tried to do as the teacher did. Instead of smiling, each of them made a face. The mixture tasted terrible.