Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Team name | Leagues | Base | Year started | Year ended | Notable riders |
| --- | --- | --- | --- | --- | --- |
| Aldershot Shots | National League Division Three | Tongham Greyhound Stadium | 1950 | 1960 |  |
| Ashfield Giants |  | Saracen Park, Glasgow | 1949 | 1952 | Ken Le Breton |
| Barrow Bombers | British League Division Two | Holker Street | 1972 | 1974 |  |
| Bradford Dukes | Elite League | Odsal Stadium | 1945 | 1997 | Listed in article |
| Bristol Bulldogs | National League, Provincial League | Knowle Stadium, Bristol | pre-1939 | 1954 | Phil Crump |
| Canterbury Crusaders | National League, British League Division Two | Kingsmead Stadium, Canterbury | 1968 | 1987 | Listed in article |
| Carmarthen Dragons |  | Carmarthen Showground, Carmarthen | 2002 | 2004 | Trevor Harding, Ben Wilson, Ben Powell |
| Cradley Heath Heathens | British League | Dudley Wood Stadium | 1947 | 1996 | Listed in article |
| Crayford Kestrels | British League Division Two/National League | Crayford Stadium, Crayford | 1968 | 1983 |  |
| Crewe Kings | British League Division Two | BR Sports Ground, Crewe | 1969 | 1975 | Listed in article |
| Ellesmere Port Gunners | British League Division Two/National League | The Stadium, Ellesmere Port | 1972 | 1982, 1985 (one season) |  |
| Exeter Falcons | Elite League, Premier League | County Ground Stadium, Exeter | 1929 | 2005 | Listed in article |
| Fleetwood Flyers | Speedway National League Division Two | Highbury Avenue Sports Stadium, Fleetwood | 1948 | 1952 |  |
| Hackney Wick Wolves | Speedway National League, | Hackney Wick Stadium | 1935 | 1939 | Listed in article |
| Hackney Hawks | British League, | Hackney Wick Stadium | 1963 | 1983 | Listed in article |
| Hackney Kestrels | Speedway National League | Hackney Wick Stadium | 1984 | 1990 | Listed in article |
| Halifax Dukes | Speedway National League, Speedway Provincial League | The Shay, Halifax | 1949 | 1985 | Eric Boocock |
| Harringay Racers | Speedway National League, division 1 | Harringay Stadium | 1947 | 1954 | Listed in article |
| Hastings Saxons | Speedway National League Division Three | Pilot Field, Hastings | 1948 | 1949 |  |
| Hull Vikings | Elite League, Premier League | Craven Park | 1995 | 2005 | Listed in article |
| Leicester Stadium | Speedway Northern League, Speedway Southern League | The Stadium, Blackbird Road, Leicester | 1929 | 1931 | Cyril "Squib" Burton, Syd Jackson |
| Leicester Super | Speedway Northern League | Leicester Super Speedway, Melton Road, Leicester | 1930 | 1931 | Fred Wilkinson |
| Leicester Hounds | Speedway National League Division Two | The Stadium, Blackbird Road, Leicester | 1937 | 1937 | Wilf Plant, Lloyd Goffe |
| Leicester Hunters | Speedway National League Division Three, Speedway Provincial League | The Stadium, Blackbird Road, Leicester | 1949 | 1962 | Ken McKinlay |
| Liverpool Chads | Speedway National League Division Three, Speedway National League Division Two, Speedway Provincial League | Stanley Stadium, Liverpool | late 1920s | 1960 | Peter Craven |
| London Lions | Speedway British League | Hackney Wick Stadium | 1986 | 1986 | See Listed in article |
| Middlesbrough Bears | Northern League, Speedway National League | Cleveland Park | 1939 | 1996 | Listed in article |
| Milton Keynes Knights |  | Groveway Greyhound Stadium, Milton Keynes | 1978 | 1992 |  |
| Motherwell Eagles |  | The Stadium, Milton Street, Motherwell | 1951 | 1954 | Listed in article |
| New Cross Rangers | Speedway National League, Speedway Provincial League | New Cross Stadium | 1937 | 1963 | Tom Farndon |
| Newport Wasps | Provincial League, British League, National League, Premier League | Hayley Stadium | 1964 (closed 1977, reopened 1997) | 2011 |  |
| Norwich Stars | Northern League, Speedway National League Division Two, Speedway National League, Division one | The Firs Stadium, Norwich | 1930 | 1964 |  |
| Nottingham | Southern League, National League | Olympic Gardens/White City Stadium, Nottingham | 1930 | 1938 |  |
| Oxford Cheetahs | Elite League, Conference League, Premier League | Oxford Stadium, Oxford | 1949 | 2007 | Listed in article |
| Paisley Lions | Speedway National League | Love Street | 1975 | 1976 | Sid and Mick Sheldrick, Alan Bridgett, Mike Fullerton, Colin Caffrey, and Stuart Mountford |
| Rayleigh Rockets | Speedway Provincial League, Metropolitan League | Rayleigh Weir Stadium, Rayleigh, Essex | 1949 | 1973 |  |
| Rochdale Hornets |  | Athletic Grounds, Greater Manchester | 1970 | 1972 | Peter Collins |
| Romford Bombers |  | Brooklands Stadium, Romford | 1969 | 1971 |  |
| Southampton Saints | Speedway National League | Banister Court Stadium, Southampton | 1928 | 1963 |  |
| Stamford Bridge Pensioners | Southern League, Speedway National League | Stamford Bridge Stadium, London | 1929 | 1932 | Gus Kuhn, Wal Phillips |
| Sunderland Stars | Speedway National League | Sunderland Greyhound Stadium, East Boldon | 1971 | 1974 |  |
| Trelawny Pitbulls | Conference League | Clay Country Moto Parc, St Austell | 2003 | 2003 |  |
| Trelawny Tigers | Premier League | Clay Country Moto Parc, St Austell | 2001 | 2003 | Chris Harris (speedway rider) |
| Walthamstow Wolves | Speedway National League | Walthamstow Stadium | 1934 | 1951 | Listed in article |
| Wembley Lions | Southern League, Speedway National League | Empire Stadium | 1929 | 1971 | Listed in article |
| West Ham Hammers | Speedway British League, Speedway National League | West Ham Stadium | 1930 | 1971 | Listed in article |
| White City Rebels | Speedway British League | White City Stadium | 1976 | 1978 | Gordon Kennett, Steve Weatherley, Trevor Geer, Marek Cieślak and Kai Niemi |
| Wimbledon Dons | Speedway National League | Wimbledon Stadium | 1929 | 2005 | Listed in article |
| Yarmouth Bloaters | Speedway National League, Speedway Provincial League | Yarmouth Stadium, Caister-on-Sea | 1948 | 1962 |  |
Question:
how many teams started before 1940?
Answer:
17