Consider the following program and select correct statements below:

$1.$ e$=$a$+$b

$2.$ f$=$c$+$d

$3.$ m$=$e$*$f

a$.$ operation $3$ depends upon results of operations $1$ and $2,$ so it cannot be calculated until both of them are completed,

b$.$ operations $1$ and $2$ do not depend on any other operation, so they can be calculated simultaneously,

c$.$ operations $1$ and $2$ depend on each other, so they cannot be calculated simultaneously,

d$.$ if we assume that each operation can be completed in one unit of time then these three instructions can be completed in a total two units of time,

e$.$ if we assume that each operation can be completed in one unit of time then these three instructions can be completed in a total one unit of time.