where do i put the dashes in this sentence... please explain why.
The number of active movie screens that is, screens showing films or booked to do so is higher now than at any time since World War II.
The number of active movie screens--that is, screens showing films or booked to do so--is higher now than at any time since World War II.
You do this because you are defining active movie screens and showing the info is not necessary.
The number of active movie screens -- that is, screens showing films or booked to do so -- is higher now than at any time since World War II.
Two "en dashes" (--) need to have spaces before and after.
Although some sources online will not take it, "em dashes" (—) can be used in the place of two en dashes.
The number of active movie screens — that is, screens showing films or booked to do so — is higher now than at any time since World War II.
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.
I hope this helps a little more.
To determine where to put the dashes in the given sentence, you need to identify the non-essential information. Non-essential information can be removed from the sentence without affecting its essential meaning or grammar.
In this case, the non-essential information is "screens showing films or booked to do so." This additional information is not necessary to understand the main point of the sentence, which is "The number of active movie screens is higher now than at any time since World War II."
To indicate non-essential information, you can use dashes (-) or parentheses (()). In this case, we will use dashes.
Here is the sentence with the dashes added:
The number of active movie screens - that is, screens showing films or booked to do so - is higher now than at any time since World War II.
The dashes help to set off the non-essential information, showing that it provides additional clarification or explanation but is not necessary for the main sentence structure or meaning.