The equivalent resistance between A and B as shown in figure is [Figure: a line from A passes 20 kΩ to point C, then another 20 kΩ to point D, then 10 kΩ to B. A plain wire joins the junction next to A directly to D, and another plain wire joins C directly to B.]

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(3) 5 kΩ. The wire from A to D makes D the same node as A; the wire from C to B makes C the same node as B. First 20 kΩ: from A to C, that is from A to B. Second 20 kΩ: from C to D, that is from B to A. 10 kΩ: from D to B, that is from A to B. All three are in parallel: 1/R=1/(20)+1/(20)+1/(10)=1/5 R_AB=5 kΩ

The equivalent resistance between A and B as shown in figure is [Figure: a line from A passes 20 kΩ to point C, then another 20 kΩ to point D, then 10 kΩ to B. A plain wire joins the junction next to A directly to D, and another plain wire joins C directly to B.]

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Why the other options are wrong