Explanation:
The CURSOR_SPACE_FOR_TIME init.ora parameter influences library cache activity. When a user needs to parse and execute a SQL statement, Oracle may eliminate an existing SQL execution plan from the library cache to make room for the new one if CURSOR_SPACE_FOR_TIME is set to FALSE, the default. However, the problem here is that another process may need the execution plan to be eliminated to make room. If you set CURSOR_SPACE_FOR_TIME to TRUE, Oracle will not eliminate a parsed execution plan from the library cache until all open cursor user processes and applications using the execution plan have been closed. Library cache performance can be improved by setting CURSOR_SPACE_FOR_TIME to TRUE. However, you must be careful only to do so when your library-cache hit ratio is 100 %. If an execution miss occurs on your database when this parameter is set to TRUE and all execution plans in the library cache are associated with open cursors, your users will receive errors saying there is not enough shared memory in your database.
Incorrect Answers:

1: The TIMED_STATISTICS parameter does not relate with CURSOR_SPACE_FOR_TIME parameter.
2: The hit percentage in the library cache must be 100 %, it is not related with percentage in the buffer cache. C: There is no restriction on OPEN_CURSORS parameter for CURSOR_SPACE_FOR_TIME parameter value setting to TRUE.
Oracle 8, DBA Certification Exam Guide, Jason S. Couchman, p. 851. Chapter 18: Tuning Memory and Operating System Use

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