Complete each sentence with a word starting with the given letter and with the number of letters stated.
He has always had a r (10 letters) streak.
The army quickly crushed the r(6 letters).
Motorists regularly f (5 letters) the law.
The company was found guilty of c (12 letters) safety regulations.

Okay, let's solve this step by step, starting with the first sentence:

"He has always had a r (10 letters) streak."

To complete this sentence, we need to find a word that starts with the letter "r" and has 10 letters. One word that fits this description is "remarkable."

"The army quickly crushed the r (6 letters)."

For this sentence, we need a word beginning with the letter "r" and containing 6 letters. A possible word is "rebelled."

"Motorists regularly f (5 letters) the law."

Here, we are looking for a word starting with "f" and having 5 letters. An appropriate word is "flout."

"The company was found guilty of c (12 letters) safety regulations."

In the final sentence, we need a word starting with "c" and consisting of 12 letters. The word that fits is "contravening."

So, the completed sentences are:

"He has always had a remarkable streak."
"The army quickly crushed the rebelled."
"Motorists regularly flout the law."
"The company was found guilty of contravening safety regulations."

I hope this explanation and step-by-step solution helps you understand the process of completing the sentences using words that begin with the given letters and have the specified number of letters.