Like a "cornerstone" and a "keystone," what does the suffix "-stone" mean?

When "-sensitive" can be used?

You can use "-sensitive" with a noun to form a compound adjective! It usually means that something is sensitive to that thing. Such as, here, the program or text is sensitive to which letter case is used. So you can use it when you want to describe something as sensitive to something else. Keep in mind that it depends on the context. Some nouns are more common to use with it! Other times it could be better to say, "[something/someone] is sensitive to [something]." Ex: I'm sensitive to criticism. Ex: The photographs are light-sensitive. Ex: The microphone is sound-sensitive. So don't shout into it. Ex: My dog is sensitive to sound. Ex: The device is touch-sensitive. So you can control it with your hands.

What does "Mother of God" mean?

"Mother of God" is an exclamation used when something unbelievable or unexpected happens. Ex: Mother of God, you scared me!

Is the word "shard" common? Could you give me some examples that use this word?

A "shard" is a sharp piece of ceramic, metal, glass, or rock that has broken off from something whole. It is commonly used when referring to the broken pieces of the aforementioned materials. Ex: The cat broke the vase, causing glass shards to fly everywhere. Ex: I accidentally cut my finger on a shard of my broken mug.

Why would North American nations have relatively less strict rules about citizenship?

From what I understand, they're actually pretty strict about citizenship in the US and Canada. In the US at least, the common way is through childbirth, marriage, serving in the military, or having residency for 5 years. While that seems simple, there are so many processes and costs involved that it's usually quite challenging for people to get citizenship.

I thought "much" means a lot of amount. But why "much" is used here? Is "this much" an expression?

You're right, "much" normally refers to a large amount of something. In some cases when paired with a noun, the word "much" can be used generally to express a certain amount of something. In the case of the video here, this is how it is used. So "this much food" in this case refers to "this amount of food", which is not necessarily a large amount, but is just a certain amount that she is showing. Here's a few examples of "much" with the meaning of a general "amount": Ex: How much food do you have in your refrigerator? Ex: I've grown by this much.