The activities of a project, their duration and the precedence relationships are given in the table. For example, in a precedence relationship $”X<Y,Z”$ means that $X$ is predecessor of activities $Y$ and $Z$. The time to complete the activities along the critical path is ____ weeks.
$\begin{array}{|c|c|c|} \hline \text{Activity} & \text{Duration (Weeks)} & \text{Precedence Relationship} \\ \hline A & 5 & A<B, C, D \\ \hline B & 7 & B<E, F, G \\ \hline C & 10 & C<I \\ \hline D & 6 & D < G \\ \hline E & 3 & E < H \\ \hline F & 9 & F < I \\ \hline G & 7 & G < I \\ \hline H & 4 & H < I \\ \hline I & 2 & --- \\ \hline \end{array}$
1. $17$
2. $21$
3. $23$
4. $25$