Answer:
What did you do with the<em><u> houseplant's </u></em>I bought yesterday?
Explanation:
Apostrophe is used to show the ownership of the noun, or in other ways, to show the contracted form of the words. So, among the four options given in the question, the sentence that contains an error in its usage of the apostrophe is the first sentence- What did you do with the<em><u> houseplant's </u></em>I bought yesterday? The use of the apostrophe in the word 'houseplant's' is wrong as there is no need for any possessive form. The word 'houseplants' in the sentence rather denotes a plural form of the noun houseplant, not the possessive form of the houseplant. The other sentences' use of the apostrophe are correct, for they all denote the possessive or ownership of the noun or the contracted form of the verbs.
It was obvious that there <em><u>weren't</u></em> any donuts left from the meeting.
<em><u>It's</u></em><em> </em>a good time to reassess our strengths and weaknesses as a company.
The<em><u> janitors' </u></em>brooms need to be replaced as soon as possible.