Which one of the following are true?

$1$ Point

Grading comment:

The following checkbox options contain math elements, so you may need to read them in your screen reader's $$reading$$ or $$browse$$ mode instead of $$forms$$ or $$focus$$ mode.

Choice $1$ of $4$:

$\backslash$epsi

$\backslash$epsi is the identity element for string concatenation

Choice $2$ of $4$:

$($

a

b

c

d

e

f

$)$

R

$=$

$($

a

b

c

$)$

R

$($

d

e

f

$)$

R

$($abcdef$)$

R

$=($abc$)$

R

$($def$)$

R

Choice $3$ of $4$:

$($

a

b

c

$)$

R

$=$

c

$($

a

b

$)$

R

$($abc$)$

R

$=$c$($ab$)$

R

Choice $4$ of $4$:

$($

w

R

$)$

n

$=$

$($

w

n

$)$

R

$($w

R

$)$

n

$=($w

n

$)$

R

for all n