10．下列运算正确的是（ ）
| A． | $（3-2\sqrt{3}）（3+2\sqrt{3}）={3^2}$-2×3=3 | B． | $（2\sqrt{a}+\sqrt{b}）（\sqrt{a}-\sqrt{b}）=2a-b$ | ||
| C． | ${（3-2\sqrt{3}）^2}={3^2}-{（2\sqrt{3}）^2}$=9-12=-3 | D． | $（\sqrt{a}+\sqrt{a-1}）（\sqrt{a}-\sqrt{a-1}）={（\sqrt{a}）^2}-{（\sqrt{a-1}）^2}$=a-（a-1）=1 |
9．当$\sqrt{x}+\sqrt{y}=\sqrt{5}-\sqrt{3}，\sqrt{xy}=\sqrt{15}-\sqrt{3}$时，x+y的值为（ ）
0 309792 309800 309806 309810 309816 309818 309822 309828 309830 309836 309842 309846 309848 309852 309858 309860 309866 309870 309872 309876 309878 309882 309884 309886 309887 309888 309890 309891 309892 309894 309896 309900 309902 309906 309908 309912 309918 309920 309926 309930 309932 309936 309942 309948 309950 309956 309960 309962 309968 309972 309978 309986 366461
| A． | 2 | B． | 5 | C． | $8-2\sqrt{15}$ | D． | $8-4\sqrt{15}+2\sqrt{3}$ |