已知 f (t)，为求<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202101/1fb776d0006a4eb2b93e07afcad58896.png" />则下列运算正确的是（其中<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202101/ada31d4207fe47d4908574b0a478486b.png" />， a 为正数）（ ） A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202101/fb0a09472a6b4408b3e833c2568308db.png" />左移<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202101/ada31d4207fe47d4908574b0a478486b.png" /> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202101/fb0a09472a6b4408b3e833c2568308db.png" />右移 C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202101/06dbb96ce1044280b13167a33033e4c6.png" />左移<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202101/ada31d4207fe47d4908574b0a478486b.png" /> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202101/06dbb96ce1044280b13167a33033e4c6.png" />右移