Can someone me ? ?

1-which of the following represents a chord but not a diameter of the circle?
a)tr
b)sn
c)pm
d)sm

2-which of the following is a semicircle
a)ts
b)tsr
c)sr
d)srn

3-if the length of the diameter of the circle is 15 inches what is the length of the radius of the circle
a)7.5 inches
b)15 inches
c)30 inches
d)any length between 0and 15

4-which of these arcs is the largest
a)nr
b)nrs
c)nst
d)np