Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Poll Source | Dates administered | Democrat: Tom Harkin | Republican: Christopher Reed | Lead Margin |
| --- | --- | --- | --- | --- |
| Survey USA | October 28-October 29, 2008 | 61% | 35% | 26.0 |
| Rasmussen Reports | October 23, 2008 | 57% | 41% | 16.0 |
| Rasmussen Reports | September 25, 2008 | 54% | 40% | 14.0 |
| Survey USA | September 17-September 18, 2008 | 60% | 37% | 23.0 |
| Des Moines Register/ Selzer & Co | September 8-September 10, 2008 | 53% | 34% | 19.0 |
| Rasmussen Reports | August 7, 2008 | 60% | 36% | 24.0 |
| Rasmussen Reports | July 10, 2008 | 55% | 37% | 18.0 |
| Rasmussen Reports | June 10, 2008 | 53% | 37% | 16.0 |
| Research 2000 | April 21-April 23, 2008 | 59% | 20% | 39.0 |
Question:
What were the dates administered when the lead margin was larger than 14 and the poll source was Research 2000?
Answer:
April 21-April 23, 2008