Rút gọn A = $\sqrt {{{\left( {\sqrt 5 - 2} \right)}^2}} + \sqrt {{{\left( {\sqrt 5 - 3} \right)}^2}}$; B = $\sqrt {7 - 2\sqrt {10} } - \sqrt {6 - 2\sqrt 5 }$; C = $\left( {4 + \sqrt {15} } \right)\left( {\sqrt {10} - \sqrt 6 } \right)\sqrt {4 - \sqrt {15} }$.