How come "was" used? not "were"?

As a verb, what does "sponsor [someone/something]" mean?

To "sponsor [someone/something]" means to provide financial support or funds to them. Here, it implies covering all the costs involved for one's parents. In commercial businesses, to "sponsor" someone or something usually means to show support to an organization, activity, event, individual, or nonprofit as a form of financial contribution. In this case, the sponsor's name or business is often shown somewhere. Ex: Adidas was a big sponsor of the World Cup in Qatar. Ex: Red Bull sponsors a Formula 1 team. Ex: I sponsored my father to get a visa here. Ex: Max said she'll sponsor your trip to Italy this year.

What does "bend over backwards" mean?

To "bend over backwards" means to go out of one's way or make every possible effort to work hard, achieve something, or do something for someone else. Ex: I've bent over backwards trying to make you happy. Ex: He bent over backwards helping me study for the test.

What's the main difference between a "rule" and a "regulation?"

Good question! The difference is where they come from. Rules are guidelines and instructions for action, and are created to manage behavior within an organization or country. They are like written principles. Meanwhile, regulations are legal rules made in addition to the laws in a country. They are legally-binding. Thus, a rule can be an instruction given by a company or organization, whereas a regulation is a rule that is given by the state. Ex: There are some internal rules to learn within this company. Ex: The government is implementing new pandemic regulations.

What makes the difference between "particular" and "certain"? Or are they interchangeable?

These words can be used interchangeably, but not in all circumstances. "Particular" in this context means "specific." If you replaced it with "certain," that would be a grammatically correct sentence that means essentially the same thing. When "particular" and "certain" are used to specify something, they are interchangeable in some but not all circumstances. Even when they mean the same thing grammatically, they are not always interchangeable. Both words have multiple definitions. "Particular" can also mean to be detailed-oriented, to want something done a certain way, meticulous. "Certain" also means to know something for sure, confident, specific, or some but not all. Ex: He is very particular about how he cleans his car. => detail-oriented Ex: Are you looking for anything in particular? => specific (grammatically can't interchange it with "certain") Ex: Are you certain about this? => confident Ex: She uses certain/particular spices in her recipes. => specific (can be used interchangeably)

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

"-Stone" is not really a recognizable or standard suffix, it just happens to be the ending of the two words here. My guess is this comes from the concept that stone is the foundation to many types of structures or buildings, so over time it came to represent the heart or basis of many things. This is why "cornerstone" and "keystone" both refer to an important quality or feature on which a particular thing depends or is based. Ex: The Queen is the cornerstone to the Commonwealth. Ex: What do you think is the cornerstone to modern society?