call, called, is called; a small, the smaller, the smallest

The gene ________ the building block of life because it is ________ unit to carry information from one generation to another.

countable noun

adverbial

Using inversion:

I didn't understand the true state of the affairs until I had read the report.

Explain the relationship between tense and time.

Using extraposition:

To wear a respirator mask when you're working with fiberglass might be a good idea.

Using transferred negation:

I think that John won't come to the party tomorrow.

Reinforcing the negation:

No passenger survived in the aricrash last week.

Using coordination:

I caught the Eurostar train from London to Paris for the weekend. Then I flew back from Paris to London with British Airways.

Using a relative clause:

She is a professor I know. She can give you advice.

Using subordination:

He smokes heavily and is now suffering from lung cancer.