Bear in mind that when a is followed by the, something specific is involved. Also, a is for a general idea but the plural countable noun can also be for a general idea. They both become "the" after their specificity is established.
Just try to keep in mind: a= general, the=specific.
Countable nouns are either a or plural as in:
Do you have a television in your house?
Yes, I have a television.
Now, it will shift to the: Is the television yours?
ANSWER: Yes, the television is mine.
Do you have televisions in your house?
Yes, I have televisions in my house.
SHIFT: Are the televisions yours?
If you remember this pattern, you should be pretty much set. [idiom: to be set]
Often, people who speak certain Slavic languages such as Russian find this pattern useful.
an em-dash and the adjacent words [fine, those specific adjacent words]
an em-dash and an adjacent word [a generality, singular]
an em-dash and adjacent words. [a generality, plural]
em-dashes and adjacent words. [a generality, all plural]
a word and a question mark [generality]
a word and the question mark [specific, the question mark after some word]
words and questions marks [generality, not very well expressed...]