单项选择题The right order of reading data in HDFS. a) Distributed Filesystem makes an RPC call to the namenode to determine location of datanodes where files are stored in form of blocks. For each block, the namenode returns address of datanodes (metadata of blocks and datanodes) that have a copy of block. Datanodes are sorted according to proximity (depending of network topology information). b) The client opens the file by calling open () method on Distributed Filesystem. c) The client then calls read () on the stream. DFSInputStream, which has stored the datanode addresses for the first few blocks in the file, then connects to the first (closest) datanode for the first block in the file. d) The Distributed Filesystem returns an FSDataInputStream (an input stream that supports file seeks) to the client for it to read data from. FSDataInputStream in turn wraps a DFSInputStream, which manages the datanode and namenode I O. e) Data is streamed from the datanode back to the client (in the form of packets) and read () is repeatedly called on the stream by client. f) When the client has finished reading, it calls close () on the FSDataInputStream g) When the end of the block is reached, DFSInputStream will close the connection to the datanode, then find the best datanode for the next block. A、ABDCEGF B、BADCEGF C、BADCEFG D、BACDEGF