Caster Semenya will get to answer one of the big track and field questions tonight: just how fast can she go in the 400m? The 800m Olympic champion, who pulled out of the one-lap race at the Rio Games, will make her Diamond League debut in this event at the Memorial Van Damme in Brussels.There has been speculation in some quarters that Semenya could have won the Olympic 400m crown had she chosen to race in this event.But the 50.74sec personal best she set in Stellenbosch in April would have been good enough for only sixth spot in Brazil.A diving Shaunae Miller of the Bahamas won in 49.44 ahead of American Allyson Felix.Neither of them will be in action tonight, but bronze medallist Shericka Jackson of Jamaica (49.85) will be, alongside American Courtney Okolo, whose 49.71 ranks her third in the world.Of the nine-woman field, five have season's bests faster than Semenya's, and three of them, American Natasha Hastings being the third, have dipped beneath 50 seconds this year.Stephenie Ann McPherson, the second Jamaican in the field, last went under 50 in 2013, although her best this year is still a respectable 50.04.Semenya, the newly crowned 800m Diamond League race winner, will have a good chance to go faster, but the question remains - by how much?Expect Semenya to be no faster than 49-high.Luvo Manyonga, South Africa's silver medallist in the long jump, returns to action tonight. Other South African competitors are 400m hurdler Wenda Nel and sprinter Carina Horn in the 100m...