Thank you all for the replies.
@jremington, I read it else where that the center wire need to be cut to make it bipolar. but why? I never intended to use the center (red) wire any way, also what is the different between not using and cut it? After I cut it I still getting the sam result, any two wires still getting the same resistance. Shouldn't it be only two resistances for the two windings? Like blue and yellow have one resistance, orange and pink have another one but blue and pink and yellow and orange has none? Unless there are some internal wiring I don't know of.BTW, I am using a L293D, not a ULN2003 or any others.