No, it's not necessary.
Yes, a comma is needed in the sentence to separate the two independent clauses. It should be: "You could not go back to work until you understood your task."
The comma goes before "therefore" when it is used to connect two independent clauses. The semicolon goes before "therefore" when it is used to separate two closely related independent clauses.
It is correct, but it can be more concise. You can say "Tell her to call me when you get back home."
Neither is correct, first because the understood subject of the verb is "you" and second "respond back" is wrong. Otherwise there is a convention about the order of pronouns and names, but it is not a grammatical rule.
The comma originated in Greece as a punctuation mark to indicate a brief pause in speech. It was later adopted by Latin writers to help clarify the meaning of sentences, and continues to be used in modern languages for clarity and organization in written text.
A homophone of back could be Bach.
2,500 years
Because you are listing, and by adding a comma, it shows the different items that you are listing.
usually b4
The comma goes before "therefore" when it is used to connect two independent clauses. The semicolon goes before "therefore" when it is used to separate two closely related independent clauses.
It is correct, but it can be more concise. You can say "Tell her to call me when you get back home."
Planking will strengthen your back, as will stretching your back; lean forward as far as you can until it hurts hold the position until for 25 seconds or longer and repeat daily until you no longer feel pain going into positions you could also lean to the side and backwards.
That varies with the problem. Could be immediate, or could take a week.
You could either wait until it grows there or get extensions
In modern writing style, it is common to use only one space after a comma when it is used as a punctuation mark. The double-spacing after a comma is a convention that dates back to the typewriter era, but it is no longer necessary with the use of modern word processing software and typesetting tools.
From North Station, take the Orange Line inbound (Forrest Hills) until you reach Back Bay station.Alternatively, you could take the Green Line inbound until you reach Copley station, which is in the Back Bay neighborhood.
There was no maximum amount of times. Someone could stay on Redemption Island until they were defeated or until they were added back into the game.
if it is an increasing pain when you breath in and out it could be texidor's twinge to cure you breath in until you "pop" it, or it could be an ache in witch massage and heat.