Consider the simple dependency matrix shown in Table $19\mathrm{.}12.$

TABLE $19\mathrm{.}12$ Simple Dependency Matrix

Which of the following statements is correct?

a$.$ The two activities are independent of each other and the project can carry out both of them immediately.

b$.A_1$ is a predecessor activity to $A_2.$

c$.A_2$ is a predecessor activity to $A_1.$

d$.$ None of these statements is correct.