Which one of the following languages over the alphabet $\{0,1\}$ is described by the regular expression: $(0+1)^*0(0+1)^*0(0+1)^*$?
1. The set of all strings containing the substring $00$
2. The set of all strings containing at most two $0$'s
3. The set of all strings containing at least two $0$'s
4. The set of all strings that begin and end with either $0$ or $1$