Here's a simple list of common, everyday adjectives in their positive, comparative and superlative forms, divided into groups to facilitate memorization.

Sigrid looks at the comparative and superlative forms of adjectives that have a "Y" or an "E" at the end, and also some that don't follow any pattern at all!

With longer adjectives, we have to add some extra words in order to form the comparative and superlative. Sigrid explains how.

Modal verbs are special verbs that go together with action verbs to indicate ability, permission, obligation and more. Let's see how they work.

Every modal verb is a bit different and not all of them can be used in all tenses. We use "may" for permission, but we can use "can" and its conditional form "could" as well.

When do we use "should" and "could"? At the end of the video, you'll also find a preview of the next 2 videos where modals are used in everyday speech for discussing probability.

Sigrid has lost a couple of important items and is trying to think where they might be. In this part, she has lost her car key. She uses plenty of modal verbs to tell her story, including modal verbs expressing probability.

Now Sigrid has also lost her glasses! In this final part, learn how to use modal verbs to express probability, and find out whether she finds the missing items.

Why do some of the national parks in the United States resemble the European Alps? Geologist Dr. Robert Darga answers this question.

Why are some rock formations and animals found on more than one continent? The explanation dates back to the Ice Age.

In Yellowstone Park, visitors can see many indigenous animals in their natural habitat and wonder at the park's natural hot springs.

Geysers represent a very popular tourist attraction in Yellowstone Park. How do they work and where do they come from? And what is sandstone? The video answers these questions.

In this segment, we learn about the role weather plays in the creation of rock formations in the national parks of the United States.

We learn more about how water interacts with the minerals in the rocks, and visit Monument Valley, a popular spot for filming westerns and commercials.

The Colorado Plateau and the Grand Canyon are just a few of the amazing geographical features of the Southwestern United States.