其它
Find the value of the expression:  $$3- \frac{6}{1 \times \left (1+2\right )}- \frac{9}{\left (1+2\right ) \times \left (1+2+3\right )}-\frac{12}{\left (1+2+3\right ) \times \left (1+2+3+4\right )}- \cdots$$  $$- \frac{60}{\left (1+2+ \cdots +19\right ) \times \left (1+2+ \cdots +20\right )}$$ 
Overseas Competition->Knowledge Point->Calculation Modules->Fractions
B 