7) you would like to display the system date in the format“20051110 14：44：17”。which select statement should you use?______。

　　a. select to_date(sydate,’yearmmdd hh:mm:ss’)from dual;

　　b. select to_char(sydate,’yearmonthday hh:mi:ss’)from dual;

　　c. select to_date(sydate,’yyyymmdd hh24:mi:ss’)from dual;

　　d. select to_char(sydate,’yyyymmdd hh24:mi:ss’)from dual;

　　e. select to_char(sydate,’yy-mm-dd hh24:mi:ss’)from dual;

　　8)which select statement will the result ‘ello world’from the string‘hello world’?______.

　　a. select substr(‘hello world’,1)from dual;

　　b. select substr(trim(‘hello world’,1,1))from dual;

　　c. select lower(substr(‘hello world’,1))from dual;

　　d. select lower(trim(‘h’from‘hello world’))from dual;

　　9)which are dml statements(choose all that apply)______.