The order of stability of the following carbocations:
`underset("I")(CH_(2)C=CH-overset(o+)CH_(2))" , "underset("II")(CH_(3)-CH_(2)-overset(o+)CH_(2))" , "underset("III")(C_(6)H_(5)-overset(o+)CH_(2))`
A. III gt I gt II
B. III gt II gt I
C. II gt III gt I
D. I gt II gt III