exercise 1 (+), exercise 2 (+), exercise 3 (+), exercise 4 (-), exercise 5 (+, -), exercise 6 (?), exercise 7 (+, -,?), exercise 8 (+, -,?)
exercise 1, exercise 2, exercise 3, exercise 4, exercise 5, exercise 6, exercise 7
exercise 1
exercise 1, exercise 2, exercise 3