Xerxes has 6, 7 and 8-arm robots in his spaceship. Unfortunately, the 7-arm robots are misprogrammed and everything they say is a lie. The other robots are fine, they always speak the truth.
Once Xerxes hears a conversation from 4 robots, but without seeing them. They talk about their arms:
The first robot claims: "We 4 have 28 arms together."
"No", says the second, "it's 27."
"Not true, 26," says the third.
"Wrong, it's 25", says the fourth and ends the conversation.
How many arms does the 4th robot have?
(A) 6
(B) 7
(C) 8
(D) 6 or 8