1, create the dropbox in the Excel 2010,
Data-> Data Validation, in the Setting, choose 'List', in the source, select the column you needs to create the dropbox, this can be selected from different work sheet.
2, Lookup function usage
VLOOKUP(lookup_value, table_array, col_index_num, [range_lookup])
Lookup_value is the value you would like to search.
table_array is source search column you need to search, can select in different worksheet or workbook
col_index_num, is the column will return the value.
range_lookup, will be the true or false, false will be exact match.