Activities $1,2,3,$ and $4$ are described in the network diagram and happen concurrently. Activity $1$ is $4$ days, Activity $2$ is $7$ days, Activity $3$ is $4$ days, and Activity $4$ is $5$ days. Which statement is most accurate?

Activity $1$ and $3$ are on the critical path.

Activity $2$ has zero float.

Activity $1$ and $3$ both have $4$ days of float.

Activities $1,3,$ and $4$ must be completed within $4$ days.