Comma

A glass of milk a cup of tea or a mug of coffee will be fine.

• A glass of milk a cup of tea, or a mug of coffee will be fine.
• A glass of milk, a cup of tea, or a mug of coffee, will be fine.
• A glass of milk, a cup of tea, or a mug of coffee will be fine.
• The sentence is correct

The gentle kind giant helped Jack climb down the vine.

• The gentle kind, giant helped Jack climb down the vine.
• The gentle ,kind, giant, helped Jack climb down the vine.
• The, gentle kind giant helped Jack climb down the vine.
• The gentle, kind giant helped Jack climb down the vine.

He will be elected tomorrow and he will be a good leader.

• He will be elected tomorrow, and he will be a good leader.
• He will be elected tomorrow and he will be a good, leader.
• He, will be elected tomorrow and he will be a good leader.
• He will be elected, tomorrow and he will be a good leader.

Mr. Pettit our school's principal will be observing the class tomorrow.

• Mr. Pettit, our school's principal will be observing the class tomorrow.

• Mr. Pettit, our school's principal, will be observing the class tomorrow.

• Mr. Pettit our school's, principal, will be observing the class tomorrow.

• Correct

Bill bought his first car on September 12 2015 and wrecked it the next day.

• Bill bought his first car, on September 12 2015, and wrecked it the next day.
• Bill bought his first car on September 12, 2015 and wrecked it the next day.
• Bill bought his first car on September 12, 2015, and wrecked it the next day.
• Bill bought his first car on September 12, 2015 and, wrecked it the next day.

My mother the lady in the pink shirt is the president of the club.

• My mother, the lady in the pink shirt, is the president of the club.
• My mother the lady in the pink shirt, is the president of the club.
• My mother the lady, in the pink shirt, is the president of the club.
• Correct

You must understand Mrs. Bingham that I am hungry for cupcakes!

• You must understand, Mrs. Bingham that I am hungry for cupcakes!
• You must understand,  Mrs. Bingham, that I am hungry for cupcakes!
• You must understand Mrs. Bingham that, I am hungry for cupcakes!
• Correct

"You're the thief" said the detective with astonishment.

• "You're the thief" said, the detective with astonishment.
• "You're the thief" ,said the detective with astonishment.
• "You're the theif," said the detective with astonishment.
• Correct

She decided to shift the responsibility onto Harry an ambitious young man.

• She decided to shift the responsibility onto Harry, an ambitious young man.
• She decided to shift the responsibility onto Harry an ambitious, young man.
• She decided to shift the responsibility, onto Harry an ambitious young man.
• Correct

On July 20 1983 an amazing woman was born. 

• On July 20, 1983, an amazing woman was born. 
• On July 20 1983, an amazing woman was born. 
• On July, 20 1983 an amazing woman was born. 
• On July ,20 1983 ,an amazing woman was born.