How many different years did Marty McFly travel to in all of the Back to the Future movies?
4
3
3
2
3
4
2
5
3
4
2
5
3
4
2
5
3
4
2
5
3
1
4
2
5
3
1
4
2
5
3
1
4
2
5
3
1
4
2
5
3
1
4
0
2
5
3
1
4
2
7
0
5
6
3
1
4
2
7
5
6
3
0
1
4
2
7
5
6
3
1
4
2
7
5
6
3
1
4
2
7
5
6
3
1
4
2
7
5
6
3
1
4
2
7
5
6
3
1
4
2
7
5
6
3
1
8
4
2
7
5
6
1
8
4
2
7
5
6
1
8
4
7
5
6
1
8
10
9
7
6
1
8
10
9
7
6
1
8
10
9
11
12
13
7
6
1
8
10
9
11
12
13
7
6
8
10
9
11
12
13
7
6
8
10
9
11
12
13
7
6
8
14
10
9
11
12
13
7
6
8
14
10
9
11
12
13
7
6
8
14
10
20
20
2 years
4 years
3 years
7 years
5 years
2 years
4 years