flashpulse: If evolution was true, the venomous snake would have died of its own venom when "evolving".
Maybe some type of snake did at some point "die of its own venom" or somehow else proved to be unsustainable. So the other kind of snakes that didn't have the same deficiency, thrived and took over.
Evolution is not a direct line, it is branching tree where many branches turn out to be unsustainable, and just die out, There were lots of different human-like creatures that coped with the world differently, but most of them died out at some point, usually because they couldn't adapt to the changing environment, or simply proved out to be inferior to some other race or species in the area. Human bringing wild dogs and rats to Australia was one kind of evolution (where humans had their part), which put some Australian species in danger. They had no means to cope with the new species.
New variations come with slight mutations. Most of them turn out to be unsustainable and die out (dying branch), some might prove to be useful and get more prevalent over time.
As for "fruits have just the right vitamins for humans and people", that is also part of evolution where both fruits and animals have evolved to benefit each other. If an animal cannot eat the fruits, it dies out (if it has no other food source), while the species which could use the plants/fruits the best, thrive the best. Similarly, for many plants it is beneficial that animals eat its fruits, and dump the seeds far away from the first plant. If animals chose to carry certain fruit seeds more than others that way, that plant would benefit (unless there is some other way for the plant to plant its seeds elsewhere, e.g. dandelion certainly doesn't need animals to throw around its seeds, it uses wind instead).
We can see evolution at work best with viruses and bacteria, as the mutations changing them are faster there so we can perceive them (unlike how e.g. humans or apes gradually change over millions of years). They mutate to cope better against e.g. antibiotics (ie. the bacteria which die of antibiotics easily do so, while variations of them which don't thrive). Also, sometimes there is bacteria or virus that kills its carriers fast, but those are pretty short-lived as without carriers such virus or bacteria can't live that long either.
So, the virus and bacteria which can live inside its carrier, maybe even benefitting it, thrive the best. Take for example the bacteria in your intestines (beneficial to you), or the herpes virus that most people carry (not beneficial AFAIK, but causes very little if any problems for most people, and transmits easily => a successful virus that thrives).
No need for "intelligent design" in any of that.