When 2 words in a row contains "s" at the end, you put an apostrophe at the end of the first word containing "s" at the end in that specific word
In, "<span>I watched a trees' branches sway in the wind," <em>"trees" </em>and <em>"branches" </em>are the words containing<em> s</em> at the end of the word in a row.
And the first word containing <em>s </em>at the end is <u />"trees," so you put in an apostrophe as it is in choice D So yes, i agree with what the other one says. It is D. </span>