Opposite angles of a cyclic quadrilateral add to 180: find an angle or expression

1. A.
   $90^\circ$
2. B.
   $135^\circ$
3. C.
   $180^\circ$
4. D.
   $270^\circ$

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1. A.
   $2$
2. B.
   $1$
3. C.
   $0$
4. D.
   $-1$

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1. A.
   $200^\circ$
2. B.
   $190^\circ$
3. C.
   $180^\circ$
4. D.
   $170^\circ$

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