Which statement is true about the execution of the command?

If you run the command the way it is will not work, because you need to specify the directory parameter, it is required, I tested and prove that it did not work. To work needed to specify the directory, I believe it is to log generation.

Here evidence.

[oracle@localhost dump1]$ expdp SYSTEM FULL=YES DUMPFILE=dpump_dir1:full%U.dmp,dpump_dir2:full2%U.dmp,dpump_dir3:full3%U.dmp FILESIZE=50M PARALLEL=3 JOB_NAME=expfull

Export: Release 12.1.0.2.0 – Production on Mon May 30 22:07:52 2016

Copyright (c) 1982, 2014, Oracle and/or its affiliates. All rights reserved.
Password:

Connected to: Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 – 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
ORA-39002: invalid operation
ORA-39070: Unable to open the log file.
ORA-29283: invalid file operation
ORA-06512: at “SYS.UTL_FILE”, line 536
ORA-29283: invalid file operation

Now adding the directory parameter can prove it works as follows:

[oracle@localhost dump1]$ expdp SYSTEM FULL=YES DUMPFILE=dpump_dir1:full%U.dmp,dpump_dir2:full2%U.dmp,dpump_dir3:full3%U.dmp FILESIZE=50M PARALLEL=3 JOB_NAME=expfull directory=DPUMP_DIR1

Export: Release 12.1.0.2.0 – Production on Mon May 30 22:09:33 2016

Copyright (c) 1982, 2014, Oracle and/or its affiliates. All rights reserved.
Password:

Connected to: Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 – 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options

WARNING: Oracle Data Pump operations are not typically needed when connected to the root or seed of a container database.

Starting “SYS”.”EXPFULL”: sys/******** AS SYSDBA FULL=YES DUMPFILE=dpump_dir1:full%U.dmp,dpump_dir2:full2%U.dmp,dpump_dir3:full3%U.dmp FILESIZE=50M PARALLEL=3 JOB_NAME=expfull directory=DPUMP_DIR1
Estimate in progress using BLOCKS method…
Processing object type DATABASE_EXPORT/EARLY_OPTIONS/VIEWS_AS_TABLES/TABLE_DATA
Processing object type DATABASE_EXPORT/NORMAL_OPTIONS/TABLE_DATA
Processing object type DATABASE_EXPORT/NORMAL_OPTIONS/VIEWS_AS_TABLES/TABLE_DATA
Total estimation using BLOCKS method: 5.578 MB
. . exported “WMSYS”.”WM$CONSTRAINTS_TABLE$”
……………………

Thus, the best answer is B.