Read the passage and answer: Household food production can make a modest but useful contribution to nutrition. Even a small balcony or shared plot can supply herbs and vegetables, but success depends on water, soil, time and local climate. Such gardens cannot solve food insecurity by themselves; income, access to markets and public support also matter. Their value is greatest when they complement, rather than replace, broader food systems. The pronoun 'Their' in the final sentence refers to:

1. Markets alone
2. Public support alone
3. Household gardens
4. Local climates