Answer:
D. Both a and c
Step-by-step explanation:
Irrational numbers can not written in a fraction form
For A, since pi is a irrational number, 2 time of it still make it irrational
For B, 6.875 could be written in fraction as 6785/1000, a rational number
For C, the number can not expressed in a fraction form because it goes on indefinite, an irrational number.