What is inappropriate in this frequency distribution?

Lower Limit: 18,30,42,54,67

Upper Limit: 29,41,53,65,78

Frequency: 11,15,22,0,2

a.There cannot be a frequency of0

b.The classes overlap

c.unequal class width

d.There is a gap

e.None of these-it is done properly

-THERE MAY BE MORE THAN ONE COR-RECT ANSWER