Which of these pairs of fractions are equivalent? 
选项为:A:$$3\frac{1}{2}$$ and $$2\frac{1}{4}$$  B:$$1\frac{1}{3}$$ and $$\frac{8}{6}$$  C:$$1\frac{1}{4}$$ and $$\frac{3}{4}$$  D:$$3\frac{3}{9}$$ and $$\frac{9}{9}$$  请回答其中一个选项.