An option which can be exercised any desired time before an expiry date is classified as

The correct answer is: D. American option.

An American option is an option that can be exercised at any time up to and including the expiration date. A European option, on the other hand, can only be exercised on the expiration date. Australian options are similar to American options, but they can only be exercised on the last trading day before the expiration date. Money options are options that are in the money, meaning that the strike price is below the market price for a call option or above the market price for a put option.

Here is a table that summarizes the key differences between American and European options:

| Option type | Exercise date |
| — | — |
| American option | Any time up to and including the expiration date |
| European option | Only on the expiration date |

Here is a table that summarizes the key differences between American and Australian options:

| Option type | Exercise date |
| — | — |
| American option | Any time up to and including the expiration date |
| Australian option | Only on the last trading day before the expiration date |

Here is a table that summarizes the key differences between American, European, and money options:

| Option type | Exercise date | In the money? |
| — | — | — |
| American option | Any time up to and including the expiration date | Yes |
| European option | Only on the expiration date | Yes |
| Money option | Any time up to and including the expiration date | Yes |

I hope this helps! Let me know if you have any other questions.