选D
∵T=2π/[(2k+1)/3]*π=6/(2k+1) (a+3)-a=3
又因每一周期内出现5/4值时有2次,出现4次取2个周期,出现8次应有4个周期
∴有4T≥3且2T≤3
即3/4≤T≤3/2
∴ 3/4≤6/(2k+1) ≤3/2
解得3/2≤k≤7/2
∵k∈N,∴k=2或3
选D
∵T=2π/[(2k+1)/3]*π=6/(2k+1) (a+3)-a=3
又因每一周期内出现5/4值时有2次,出现4次取2个周期,出现8次应有4个周期
∴有4T≥3且2T≤3
即3/4≤T≤3/2
∴ 3/4≤6/(2k+1) ≤3/2
解得3/2≤k≤7/2
∵k∈N,∴k=2或3