The set of all strings over ‚Äö√Ñ√∂‚à ö‚Ć‚à ö¬¥ = {a,b} in which all strings having bbbb as substring is$

• A. (a+b)* bbbb (a+b)*
• B. (a+b)* bb (a+b)*bb
• C. bbb(a+b)*
• D. bb (a+b)*