Clean or to clean

[hoangkha]

Hi!
- Jasmine is working as a dental assitant. What she does is.................. people's teeth.
[FONT=MathJax_Math]A[FONT=MathJax_Main].[/FONT][/FONT] clean [FONT=MathJax_Math]B[FONT=MathJax_Main].[/FONT][/FONT] cleans [FONT=MathJax_Math]C[FONT=MathJax_Main].[/FONT][/FONT] cleaning [FONT=MathJax_Math]D[FONT=MathJax_Main].[/FONT][/FONT] to clean
The key is A, but I am wondering why D is wrong, please?

 

[Soup Chicken]

Not a teacher

You could say "Her job is to clean people's teeth" or "Her job is cleaning people's teeth".
I don't know why it is wrong (the rules involved), but it most definitely sounds wrong to me.

 

[Ali Hsn]

Hello!

*I AM NOT A TEACHER OR NATIVE.*

Hi!
- Jasmine is working as a dental assitant. What she does is.................. people's teeth.
[FONT=MathJax_Math]A[FONT=MathJax_Main].[/FONT][/FONT] clean [FONT=MathJax_Math]B[FONT=MathJax_Main].[/FONT][/FONT] cleans [FONT=MathJax_Math]C[FONT=MathJax_Main].[/FONT][/FONT] cleaning [FONT=MathJax_Math]D[FONT=MathJax_Main].[/FONT][/FONT] to clean
The key is A, but I am wondering why D is wrong, please?

In my opinion, that's because of the verb which follows the subject. The to-infinitive comes after some certain verbs such as decide, like, want, etc. (please, see the second link below).
Therefore, if your sentence was "What she wants is...................... their rooms", then you had to fill in the blank with "to clean".

http://learnenglish.britishcouncil.org/en/english-grammar/verbs/infinitive
http://learnenglish.britishcouncil.org/en/node/1404/

 

[tzfujimino]

Hi!
- Jasmine is working as a dental assitant. What she does is.................. people's teeth.
[FONT=MathJax_Math]A[FONT=MathJax_Main].[/FONT][/FONT] clean [FONT=MathJax_Math]B[FONT=MathJax_Main].[/FONT][/FONT] cleans [FONT=MathJax_Math]C[FONT=MathJax_Main].[/FONT][/FONT] cleaning [FONT=MathJax_Math]D[FONT=MathJax_Main].[/FONT][/FONT] to clean
The key is A, but I am wondering why D is wrong, please?

Hello.:-D
We need a subject complement after the linking verb 'is'.
In your example, we need something that functions as a noun - a 'to-infinitive' or a 'gerund', in this case.
Thus, C and D are both grammatically correct, in my opinion.

However, I often read/hear A (a bare infinitive) used in this type of construction.
I imagine that the bare infinitve (in this type of construction) is so commonly used that it has become the norm.

 

[emsr2d2]

I would use A.

 

[hoangkha]

Thank you all. I have just found this point of grammar in Practical English Usage (3rd edition) by Michael Swan, page 257.
Expressions like "All I did was, What I do is" etc can be followed by an infinitive without "to".
- All I did was (to) give him a little push.
- What a fire-door does is (to) delay the spread of a fire.

 

[Roman55]

I am not a teacher.

Yes, but the important thing to bear in mind is that this works because the verb is "do" in each case.

Replace "do" with almost any other verb, such as "want" or "be", and the "to" becomes indispensable.

All I wanted was to give him a little push.
What a fire-door is for is to delay the spread of a fire.