Average based on multiple criteria

Hi everyone,

I`m working on an evaluation sheet for tour guides at a medium sized tour company. At the end of each trip all customers are asked to fill in a short customer satisfaction research and rate different parts of the tour on a scale of 1 to 5.

All survey results are entered in an Excel sheet with the following columns:

Column A: Tour date
Column B: Destination
Column C: Guide
Column D - J: Results for organization, knowledge, friendliness etc.

Sheet 2 gives an overview of the results and the average score for each guide. However, most guides guide tours to different destinations, so now I like to calculate the results for each individual tour.

This is my formula to calculate the average score from one guide for all tours:
=AVERAGE(IF(Questionaires!$C$2:$C$5000="Bob",Questionaires!$D$2:$D$5000))

How can I modify this formula so it calculates the average from column D for only the tours to Vancouver (column B), guided by Bob(column C), and excluding the empty cells in column D?

Thanks!