pre_text: Stock-based Compensation The following table summarizes stock-based compensation expense related to RSUs, stock options, and ESPP shares for the fiscal years ended September 30, 2019, 2018, and 2017, which were allocated as follows (amounts shown in thousands):
table: 2019 2018 2017
table: Cost of revenue $207 $78 $52
table: Selling and marketing 2,967 2,656 1,577
table: Research and development 2,013 1,801 1,028
table: General and administrative 4,450 4,415 2,821
table: Stock-based compensation expense included in expenses $9,637 $8,950 $5,478
question: Analyse this data from a financial earnings document. What is the average expense of general and administrative from 2017 to 2019?