WWF stands for

Concept: The expanded form of an international organisation's abbreviation is fixed by its own founding history and official charter, not by whichever words the letters could plausibly stand for. Some organisations keep their original founding name in certain regions even after a later global rename, so both the founding name and the renamed form can be seen in reference material.

Application: WWF was founded in 1961 under the name World Wildlife Fund. In 1986 the organisation adopted the new global name World Wide Fund for Nature, but it continued to use World Wildlife Fund in the United States and Canada. In general-awareness usage — and among the options offered here — the expected expansion of WWF is World Wildlife Fund.

Cross-check: Testing each option against the organisation's actual history/name confirms the choice:

• World Wide Fund is only a partial phrase — the full renamed form is "World Wide Fund for Nature"; dropping "for Nature" does not match either the founding name or the correctly renamed name.

• World War Fund is not the name of any real organisation; it merely swaps in a word ("War") that sounds similar to "Wide".

• World Watch Fund does not belong to WWF either; it is easily confused with "Worldwatch Institute", a separate and unrelated environmental research organisation.

Result: World Wildlife Fund is the organisation's founding (and still official in the US/Canada) name, and is the standard expansion of WWF expected in this context.