Explanation

A basin is a depression, or dip, in the Earth's surface.

River Drainage Basins.

A river basin is made up of many different watersheds.

Explanation

"The sentence is in the present perfect tense, indicating an action that started in the past and continues to the present.

'Have resigned' is the correct phrase to use, showing that seven people left their job."

Explanation

After creating a table, fields (columns) can be modified.

It allowing for both additions and deletions as required.

Explanation

"Further" is used to indicate a deeper level of investigation.

"Most apparent" correctly suggests that something became increasingly clear.

Explanation

The correct question tag is "will you."
It politely requests the listener’s confirmation or assistance.
This matches the future-oriented tone of "If you come across my keys."

Explanation

Young : Old :: Morning : Evening

Explanation

The phrase "under the shadow of the tree" is commonly used in English to indicate sitting within the shade provided by the tree.

So, the complete sentence is: He sat under the tree's shadow.

Explanation

"So much" expresses the quantity of trouble, while "that" introduces the result of parking the car in the garage. 

The phrase "so much...that" is commonly used to indicate cause and effect.

Explanation

Straw, camphor, alcohol, petrol, diesel etc. catch fire easily to release heat energy and light energy.

So, these are examples of combustible substances.

Explanation

An optical fiber is a flexible,

transparent fiber made by drawing glass  or plastic

To a diameter slightly thicker than that of a human hair.