Please explain the mechanics of ETF briefly. In your explanation, please (a) indicate the differences and similarities between ETF and open-end and closed-end mutual fund; (b) describe the roles played by the three main parties (ETF sponsors, authorized participants, and investors) that are involved in the structure of ETF; and (c) demonstrate specifically what actions authorized participants will take when there are discrepancies between ETF prices and its intraday indicative values