You used the IMMEDIATE option to shut down your database instance. Consider the steps that mayoccur when a database instance is started and database is opened： 1：SGA is allocated. 2：Control file is read. 3：Redo log files are opened. 4：Instance recovery is started. 5：Background processes are started. 6：Data file headers are checked for consistency. 7：Server parameter file or the initialization parameter file is read. Which option has the correct order in which these steps occur（）

A. 7，1，5，2，3，6，4
B. 1，5，7，2，3，6；step 4 is not required
C. 7，1，5，2，3，6；step 4 is not required
D. 1，2，3，5，6，4；step 7 is not required