WHICH_OF_THE_FOLLOWING_REGULAR_EXPRESSIONS_REPRESENTS_THE_SET_OF_STRINGS_WHICH_DO_NOT_CONTAIN_A_SUBSTRING_‚ÄÖ√Ñ√∂‚ÀÖ√Ë‚Àւ§RT‚ÄÖ√Ñ√∂‚ÀÖ√Ë‚ÀÖ¬•_IF_‚ÄÖ√Ñ√∂‚ÀւĆ‚ÀÖ¬¥=_{R,_T}?$#

• A. (rt)*
• B. (tr)*
• C. (r*t*)
• D. (t*r*)