oracle11.2.0.1 not using optimizer

I imported oracle data from 10.2.0.4 to 11.2.0.1 by expdp and impdp after that query time slower than 10g and cost is very height.

but when I use /*+ optimizer_features_enable('11.2.0.1') */ in a statement the time and cost is too low

and then I test in another system by impdp with exclude=statistics, it using optimizer in a query

How to set the database to enable the optimizer?

here the optimizer in my parameter file

Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production

With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> show parameter optimizer;

NAME                                 TYPE        VALUE