Ten persons numbered $1,2,\dots ..,10$ play a chess tournament, each player against every other player exactly one game. It is known that no game ends in a draw. If $w_1,w_2,\dots ..,w_{10}$ are the number of games won by players $1,2,\dots ..,10$ respectively, and $l_1,l_2,\dots \dots \dots \dots .,l_{10}$ are the number of games lost by the players $1,2,\dots ..,10$ respectively, then a. $\sum w_i=\sum l_i=45$ b. $w_i+1_i=9$ c. $\sum w{l}_1^2=81+\sum l_1^2$ d. $\sum w_i^2=\sum l_i^2$

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