Identifying the Main Idea

When we think of seaweed, we usually picture brown or green plants a foot or so in length.  Seaweeds are also of other colors.  Some are red.  Some kinds grow to lengths of a hundred feet!  These form giant seaweed forests, where many kinds of fish take shelter.  What is the main idea?

Yellowstone National Park is mainly located in Wyoming, although three percent is located in the state of Montana.  The Continental Divide of North America runs diagonally through the southwestern part of the park.  The park sits on the Yellowstone Plateau, which is an average elevation of 8,000 feet above sea level.  This plateau is bounded on nearly all sides by mountain ranges.  There are 290 waterfalls that are at least fifteen feet in the park, the highest being the Lower Falls of the Yellowstone River, which falls 308 feet.  

A penny for your thoughts? If it’s a 1943 copper penny, it could be worth as much as fifty thousand dollars. In 1943, most pennies were made out of steel since copper was needed for World War II, so the 1943 copper penny is ultra-rare. Another rarity is the 1955 double die penny. These pennies were mistakenly double stamped, so they have overlapping dates and letters. If it’s uncirculated, it’d easily fetch $25,000 at an auction. Now that’s a pretty penny. 

Someday we will all have robots that will be our personal servants. They will look and behave much like real humans. We will be able to talk to these mechanical helpers and they will be able to respond in kind! Amazingly, the robots of the future will be able to learn from experience. They will be smart, strong, and untiring workers whose only goal will be to make our lives easier.
What is this selection mainly about?

Yesterday was my birthday. When I woke up, I noticed my brother Josh hung up a big sign that said,"Happy Birthday, Charles!" Mom made spaghetti for dinner.
It's my favorite food in the whole world. My friend Dave came over and handed me a wrapped gift. I wondered what it was. It was a new basketball! I had a great day.
What is the main idea of this paragraph?

Yesterday was my birthday. When I woke up, I noticed my brother Josh hung up a big sign that said,"Happy Birthday, Charles!" Mom made spaghetti for dinner.
It's my favorite food in the whole world. My friend Dave came over and handed me a wrapped gift. I wondered what it was. It was a new basketball! I had a great day.
What is the main idea of this paragraph?

Scrabble is a game that provides hours of challenging fun for you and your friends. In this game you use your letters to build new words from words already on the game board. Scrabble is a fun way to learn new words and meanings.
What is the main idea of the passage?