$$100-97+94-91+88-85+\cdots +4-1$$  $$=\left( 100-97 \right)+\left( 94-91 \right)+\left( 88-85 \right)+\cdots +\left( 4-1 \right)$$  $$=\underbrace{3+3+3+\cdots +3}_{17项}$$  $$=3\times 17$$  $$=51$$．  故选$$\text{C}$$． 
请问$$100-97+94-91+88-85+\cdots +4-1$$之值等于多少？ 
1. $$45$$ 
2. $$48$$ 
3. $$51$$ 
4. $$54$$ 
5. $$57$$ 