But what else I should know to eliminate II & III with surety ?

Dear Omair,

I have redrawn the figure you posted in such a way that it satisfies the given condition of a=b.

You need to imagine possibilities to prove option (II) and Option (III) wrong.

You can see in the following figure, 'f' & 'k' are neither parallel nor 'm' & 'f' are perpendicular.

It also satisfies all the given conditions.

So, we can conclude that, only condition (I) is true as a,c & b,d form a linear pair. Thus, a=b => c=d

**Ans: Option B**
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