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 C: 
Let's call the teams A1, A2, ..., A7, and B1, B2, ..., B7. 
Try this: 
   
    1) A1, A6;  A2, A5;  A3, A4;  A7, B7;   same pairs of Bs as pairs of As 
    2) A2, A7;  A3, A6;  A4, A5;  A1, B1;   same pairs of Bs as pairs of As 
    3) A3, A1;  A4, A7;  A5, A6;  A2, B2;   same pairs of Bs as pairs of As 
    4) A4, A2;  A5, A1;  A6, A7;  A3 B3;    same pairs of Bs as pairs of As 
    5) A5, A3;  A6, A2;  A7, A1;  A4, B4;   same pairs of Bs as pairs of As 
    6) A6, A4;  A7, A3;  A1, A2;  A5, B5;   same pairs of Bs as pairs of As 
    7) A7, A5;  A1, A4;  A2, A3;  A6, B6;   same pairs of Bs as pairs of As 
    8) A1, B2;  A2, B3; ...; A6, B6; A7, B1 
    9) A1, B3;  A2, B4; ...; A5, B7; A6, B1; A7, B2 
    10) A1, B4;  A2, B5;  A3, B5;  A4, B7;  A5, B1;  A6, B2; A7, B3 
 
The days can be used in any order. 
--Victoria 
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