You are maintaining your Oracle10g database in the UNIX environment. An application requires one of the user sessions to exist in the operating system local time zone. You decide to set the time zone for a session using the operating system environment variable. Which command will you issue？（）

A. setenv ORA_SDTZ ’DB_TZ’
B. setenv ORA_SDTZ ’+10：00’
C. setenv ORA_SDTZ ’OS-TZ’
D. setenv ORA_SDTZ ’Europe/London&rsquo