Which of the following function is/are periodic?
A. `f(x)={(1, "x is rational"),(0, "x is irrational"):}`
B. `f(x)={(x-[x], 2n ≤ x < 2n+1),(1/2, 2n+1≤x<2n+2):}`
where [.] denotes the greatest integer function n∈Z
C. `f(x)=(−1)^[(2x)/π]`, where [.] denotes the greatest integer function
D. `f(x)=x−[x+3]+tan((πx)/2)`, where [.] denotes the greatest integer function, and a is a rational number