The more the merrier

This is another way of expressing 'He who hesitates is lost' ( ... although there is a contrary proverb, 'Look before you leap'!).
Perhaps your own language also has such pairs of proverbs which cancel one another out, or at least contradict each other fairly directly in an otherwise same situation.
There may well be elements of truth in the other possible Answers, but those are not 'the traditional version'.

Answer 1 is the best: the classic description of a typical Tragic Hero (not just Icarus in the old legend). The other options sound fair enough but are not 'the proper expression', and indeed they are in increasingly weak English as you go down the list.

Galileo had worked out enough of the principles of mechanics to know that almost any massive object ~ even the Earth ~ can be moved by forces, including a lever (if it were big enough, and suitably positioned).
None of these other possible 'consequences' is quite so impressive, is it?

'They' may very well also have done all the other immediate celebratory things, but Answer 3 is the classic closing clause of many a fairy-tale in the English language.

Answer 1 is 'borrowed' from the long-running slogan of that somewhat less healthy convenience food, the Mars (R) Bar. The other two wrong answers each rhyme and mean well, but No.2 is the classic.

Answer 1 happens to be true but hardly useful or relevant! Answer 4 is the traditional correct final line.
The meaning is that any of us may do better in life to speak less and listen more (no bad thing for a language student, at any rate!)

Cars are countable, but pollution (as such) is not ... though of course, technical people can quantify its effects (amounts of airborne particles, declining numbers of live specimens in woodlands and watercourses etc.)

If you work carefully through it, only Answer 1 fits the facts: at the outset of World War Two, when flying (including military flight) was still quite a new technology, all that stood between British freedom and domination by Nazi Germany ~ along with most of the rest of mainland Europe ~ were the relatively small number of planes and pilots who kept the attacking Luftwaffe at bay. Never, as Churchill said, had the fate of such huge numbers of civilians (and others) been held and saved by such a small number of active combatants; because most previous battles had, of course, been fought 'down on the surface' between large armies and/or navies, rather than by a small number of skilled people in 'airspace'.
Answer 2 says most closely the same thing, but the moral sense of 'owing' (i.e. 'owing their lives') is lacking from this version.

Answer 2 is 'the classic' here: fine weather should be ahead for the morrow, which is more comfortable for those working out-of-doors.
Either or both of Answers 3 & 4 may happen to be true, but that doesn't make them right!

This is an old English 'jingle' (it doesn't quite rhyme, but at least the 'i'-sounds assonate), and it means that a small repair job done sooner ~ e.g. on an item of clothing ~ is better than waiting and having to do bigger repairs once the problem has grown worse. It is also used metaphorically (i.e. a minor 'word' or correction, early on, is better than allowing a situation to develop into a complete disaster!).