D

4+1=5

8-3=5

2+3=5

5+0=5

10-5=5

Minh has never climbed the Mount Fansipan

8-4=4>3

7-2=5>3

4-0=4>3

6-1=5>3

9-3=6

9-4 =5

9-5= 4 

9-6=3

9-7=2

9-8=1

\(C,\dfrac{1}{2}.\dfrac{3}{4}+\dfrac{1}{2}.\dfrac{1}{4}=\dfrac{1}{2}.\left(\dfrac{3}{4}+\dfrac{1}{4}\right)\)

\(=\dfrac{1}{2}.\dfrac{4}{4}=\dfrac{1}{2}.1=\dfrac{1}{2}\)

\(D,\dfrac{11}{3}.\dfrac{26}{7}-\dfrac{26}{7}.\dfrac{8}{3}=\dfrac{26}{7}.\left(\dfrac{11}{3}-\dfrac{8}{3}\right)\)

\(=\dfrac{26}{7}.\dfrac{3}{3}=\dfrac{26}{7}.1=\dfrac{26}{7}\)

Hoa's collection has eight hundred stamps