It depends on what species of bat you're referring to but as a blanket statement, it seems bats have the ability to limit certain responses to diseases like inflammation. It's not that bats are immune to viruses or anything, they simply have a much higher tolerance for diseases. A lot of the damage caused by illnesses is our body's reaction and how it fights it off. Things like fever which is designed to kill off infections also significantly disrupts the body and in some cases can cause as much if not more damage than the actual infection or virus.

Bats have the ability to control their body's response to diseases much more than other animals. This may also explain their relatively long lifespans. So they can act normally despite carrying a viral load that would make other animals like humans go nuts trying to get rid of it.

Productivity means different things in different contexts. The easiest way to see productivity is in something like a factory where they produce things. But in many fields productivity can be how much value you're extracting, i.e. how much money is this industry making. The assumption is, if you are charging X amount for something and people are actually buying it, it must be worth that much. This assumption is based on really old economic theory where if something is overpriced people wouldn't buy it and they'd be forced to make it cheaper to reach market equilibrium.

Another measure of productivity can be growth. We generally measure the growth of the economy based on money and jobs. How many jobs has this industry added, which can indicate they are producing more.

TLDR; To simplify, productivity can be a tier list. Are you producing more? You're being more productive. Are you making more money? You're being more productive. Are you adding more jobs? You're being more productive.

It's true that you don't know what the future holds. A lot can change in 10 years, a lot can change in just one or two years. But, I would never recommend staying in a relationship and "hoping" things will change. I tell anyone in a similar situation that you have to love your partner as they are now. You should not love a future idealized version of your partner.

If it were something small that you could just say "agree to disagree" and move on with your lives that's fine. But this under most circumstances would be a deal breaker. Find a way for your partner to understand or find someone else who will.

Sugar isn't strictly bad for us. The body uses sugar for a lot of important things like being the primary source of energy in the body. Too much of anything is bad and we just tend to have too much sugar. When we have too much sugar it throws our body out of balance and can even lead to the body not producing the natural sugars that it needs.

Cravings are the body's way of telling us we need something. When you're dehydrated you crave water because you need it. Sugar is one of the main ways we get energy so the brain sends out reward signals when we ingest sugar because it wants to keep getting high-energy foods. In nature, it's difficult to get energy-dense foods like that so it wants us to keep eating more. The problem is, with modern society we've made it too easy to get processed sugar. Ultimately, it's just too much of a good thing.