Which lines are parallel?

blue and red only
green and red only
green, blue and red
none
This is a well known Zöllner il­lu­sion, first de­scribed in 1860. It may be caused by this im­pres­sion of depth. The black lines are par­al­lel, too!

Answers distribution

blue and red only
green and red only
green, blue and red
none
answers
flagCroatia
0%
6%
86%
6%
15
flagPakistan
15%
0%
84%
0%
13
flagAustralia
0%
4%
79%
15%
44
flagSpain
5%
10%
78%
0%
19
flagthe United Arab Emirates
10%
10%
73%
5%
19
flagthe United Kingdom
4%
8%
70%
14%
306
flagPoland
4%
9%
69%
15%
9738
flagFrance
0%
8%
67%
18%
37
flagItaly
3%
14%
67%
14%
28
flagNorway
5%
15%
65%
15%
20
flagthe United States
5%
7%
64%
20%
731
flagGermany
4%
15%
64%
15%
133
flagIndonesia
0%
0%
64%
35%
14
flagthe Philippines
4%
4%
60%
28%
25
flagCanada
6%
10%
57%
22%
49
flagIndia
6%
10%
55%
23%
188
flagthe Netherlands
11%
5%
55%
23%
34
flagRepublic of Ireland
5%
11%
51%
31%
35
flagDenmark
23%
7%
46%
23%
13
flagSouth Africa
0%
31%
43%
18%
16

Gender

men67%
women73%
blue and red only
5%
4%
green and red only
10%
7%
green, blue and red
67%
73%
none
16%
14%

Language versions

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answers
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Which lines are parallel?
1467
64%

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