The spectral types of four stars are listed below. Which star has the largest radius

The spectral types of four stars are listed below. Which star has the largest radius?

A A5 V

B F5 I

C G8 III

D M0 I

E more information is needed to answer

M0I

This is a red-giant star, actually, to be precise, it's a red-supergiant (compare to VY Canis Majoris)

It could potentially be F5I, but most likely it's M0I

EDIT:

The I is a classification of the size of the star. You have I II III IV and V. The lower the roman numeral the larger the star. For instance, V means that it is a dwarf or main sequence star, like our Sun which is a G2V. The letter at the beginning is the spectral classification, and M is a red star. The number in the middle ranges from 0 - 9 which describes the position between two spectral classes on the HR diagram. Let's take the example of the Sun. The 2 in G2V means that it is 2/10 of the way to a K spectral class which is the next proceeding class of spectral type.

EDIT:

Oops... I didn't realize E was there. In this case it would be E. Since two stars are super-giants we don't know the exact size.

Studying means finding the answer, not getting someone else to get it for you.

Its not hard to do a bit of searching to get the information you're looking for:
http://en.wikipedia.org/wiki/Stellar_cla…

Why it'll be the A5 V, or at least that will give you the mark you deserve.