把本地计算机当前目录下的文件csdn.txt复制到远程计算机的/tmp目录下的正确命令是()

A. scp ./csdn.txt root@remotehost:/tmp
B. scp root@remotehost:/tmp ./csdn.txt
C. scp localhost:/csdn.txt remotehost:/tmp
D. scpremotehost:/tmp localhost:/csdn.txt