Which verb agrees with its subject? there is nothing i more than the chance to sing this song in the spring concert. a. is wanting b. want c. has wanted d. wants

There is nothing I want more than the chance to sing this Song in the Spring concert. This verb agrees with its subject. 

The answer is "...nothing I want more than the chance to sing..." When you're not sure, simply take the subject (I) and match it with each of the predates and see which one sounds right. 
I is wanting no
I want yes
I has wanted.. no
I wants no

(The answer is B.)

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