The correct answer is `They were demanding more direct elections in Hong Kong`. Option 4 refers to a significant protest in Hong Kong`s history that occurred in 2003, with about half a million people participated. The march was prompted by dissatisfaction with the city`s Beijing-backed leadership, and a desire for more democratic processes. In contrast, Options 1, 2, and 3 are not accurate. Option 1, calling for tax relief, was not the reason for this specific protest. Option 2, referring to an objection to a security law, is plausible as there have been protests in Hong Kong over security laws, but it was not the cause for this 2003 march. Option 3, mentioning the Falun Gong religious group, is also incorrect as the group was not the main organizer of the demonstration.