Gill Gross answers your comments, including: is Frances Tiafoe correct that tennis is the hardest sport in the world, can Daniil Medvedev repeat last year's Sunshine Double success, why do Czech Republic and Russia produce so many stars, should there be a January Masters 1000, has Medvedev's career already been a success, what can Gilles Simon add to Medvedev's team, how can lower ranked players earn a better living in tennis, are sparse crowds in Middle East tournaments a problem, why have Andy Murray and Stan Wawrinka's nerve management gotten worse with age, why has Lorenzo Musetti struggled recently, should Naomi Osaka and Emma Raducanu be taking wildcards and who is most likely to win the Sunshine Double?