Having more than the usual numbers of fingers or toes on the hands or feet is termed polydactyly.
A. Having more than the usual numbers of fingers or toes
B. Having had more than the usual number of fingers or toes
C. Having more than the usual number of fingers or toes
D. To have more than the usual number of fingers or toes
E. To have more than the usual numbers of fingers or toes

What is the subject in this sentence? it is polydactyly NOT numbers fingers toes hands, etc. notice the sentence is written in passive tense. So if we are to follow the active voice which is subject verb object then this sentence should be:

The term polydactyly is having more than the usual numbers of fingers or toes on the hands or feet.

Notice that having is much more appropriate in this scenario than to have. "The term polydactly is to have more than..." sounds awkward and and not as concise as having.

Did you know how to choose between the word number of numbers?

Infinitives and Gerunds are always a nice catch.
A small tip - invert the sentence and test.

C: Polydactyly is termed as having abcd
D: Polydactyly is termed as to have abcd ( Awkward )

Chose C over D.

PGMAT wrote:Having more than the usual numbers of fingers or toes on the hands or feet is termed polydactyly.
A. Having more than the usual numbers of fingers or toes
B. Having had more than the usual number of fingers or toes
C. Having more than the usual number of fingers or toes
D. To have more than the usual number of fingers or toes
E. To have more than the usual numbers of fingers or toes


C

Can some one explain why D is incorrect. This is mgmat cat question. Why 'to have' is not acceptable? We are stating some thing general here.

The prepositions built into infinitives make them automatically more "wordy" and sometimes less clear. Sometimes they are the only option, sometimes one of several. There are plenty of examples, though, of the infinitive being used as a verbal noun in English -- "To err is human" or "To know me is to love me" -- so it's not incorrect on the basis of grammar.