50. According to the article, which of the following is true? (A) Arnall’s two formulas pointed to July 20th and June 29th respectively as the happiest day. (B) Arnall himself admitted that what’s more important is to find out the factors of happiness. (C) The most crucial element of the two happiest dates proposed by Arnall was longer daytime. (D) The happiest date calculated by Arnall in 2016 could apply to UK and many other countries.