Assume that we have a single process operating system. The operating system consists of just one process. Each application program will run as a thread within the process. Which of the following are correct?

$($a$)$ The application programs can communicate with each other via shared memory

$($b$)$ The application programs can communicate with each other via message passing

$($c$)$ The application programs need to trust each other because they may access the files opened by each other

$($d$)$ The application programs cannot run on different processor cores

$($e$)$ When application program initiates a blocking I$/$O$,$ the other application programs will have to wait for the I$/)$ to complete first before they can perform any I$/$O operations