From Largest to smallest unit of measure:
KILO means 1000
HECTO means 100
DEKA means 10
DECI means 1/10
CENTI means 1/100
MILLI means 1/1000
Accordingly, the answer is 4 or D, for Centi. Of the options provided Centi is the smallest unit of measure. Width is a red herring to confuse you.