数列\(\{a _{n} \}\)满足\(a _{n+1} =\sin a _{n}\)，\(a _{1} =a(a > 0)\)，则\((\:\:\:\:)\)
A. \(a _{n+1} \geqslant a _{n}\)
B. \(a _{n+1} \leqslant a _{n}\) C. \(a=3\)时，\(a _{n+1} -a _{n} \geqslant a _{n} -a _{n-1}\) D. \(a=4\)时，\(a _{n+1} -a _{n} \geqslant a _{n} -a _{n-1}\)
