1. My uncle visited us this weekend.
2 I listened to music with friends.
3 We studied hard for the exam. So, we answered all the questions.
4 "Did you finish your homework?" "No, I did not. "
5 I waited for the school bus but it did not come.
6 Karen asked for help to finish her homework.
7 Did you invite them to your party last week.
8 Yesterday night, somebody knocked at the door. But I did not open it.
9 The students walked down the street with their teachers.
10 Something strange happened last night.
11 Tom checked his answers.
12 The postman delivered the letters.
13 We lived in Madrid three years ago.
14 Helen did not study for the exam, and she failed.
when both valves are closed (passive).
2) The piston must be connected (passive) to a mechanism,
which controls (active) it's sliding.