Please read the following table in HTML format from a webpage and then answer the question in detail according to the table. Each table cell is defined by a <td> and a </td> tag. Each table row starts with a <tr> and ends with a </tr> tag. 'rowspan=m' and 'colspan=n' represents a cell spaning over 'm' rows and 'n' columns.

Webpage title:
Six Flags Discovery Kingdom
Table title:
Roller coasters
Table:
<table id='hittask' contenteditable='False'>
<tr> <th colspan=1 rowspan=1 > Name </th><th colspan=1 rowspan=1 > Manufacturer </th><th colspan=1 rowspan=1 > Opened </th><th colspan=1 rowspan=1 > Model name </th><th colspan=1 rowspan=1 > Location </th></tr>
<tr> <td colspan=1 rowspan=1 > Batman: The Ride </td><td colspan=1 rowspan=1 > S&S Worldwide </td><td colspan=1 rowspan=1 > 2019 (Under construction) </td><td colspan=1 rowspan=1 > 4-D Free Spin </td><td colspan=1 rowspan=1 > DC Universe </td></tr>
<tr> <td class="highlighted"  colspan=1 rowspan=1 > Boomerang: Coast to Coaster </td><td colspan=1 rowspan=1 > Vekoma </td><td class="highlighted"  colspan=1 rowspan=1 > 1998 </td><td colspan=1 rowspan=1 > Boomerang </td><td colspan=1 rowspan=1 > Sky </td></tr>
<tr> <td class="highlighted"  colspan=1 rowspan=1 > Kong </td><td colspan=1 rowspan=1 > Vekoma </td><td class="highlighted"  colspan=1 rowspan=1 > 1998 </td><td colspan=1 rowspan=1 > SLC (689m Standard) </td><td colspan=1 rowspan=1 > Sky </td></tr>
<tr> <td colspan=1 rowspan=1 > Medusa </td><td colspan=1 rowspan=1 > Bolliger & Mabillard </td><td colspan=1 rowspan=1 > 2000 </td><td colspan=1 rowspan=1 > Floorless Coaster </td><td colspan=1 rowspan=1 > Sky </td></tr>
<tr> <td colspan=1 rowspan=1 > The Flash: Vertical Velocity </td><td colspan=1 rowspan=1 > Intamin </td><td colspan=1 rowspan=1 > 2001 </td><td colspan=1 rowspan=1 > Twisted Impulse Coaster </td><td colspan=1 rowspan=1 > DC Universe </td></tr>
<tr> <td colspan=1 rowspan=1 > Cobra </td><td colspan=1 rowspan=1 > Zierer </td><td colspan=1 rowspan=1 > 2000 </td><td colspan=1 rowspan=1 > Tivoli - Large </td><td colspan=1 rowspan=1 > Sky </td></tr>
<tr> <td colspan=1 rowspan=1 > Roadrunner Express </td><td colspan=1 rowspan=1 > Zamperla </td><td colspan=1 rowspan=1 > 1999 </td><td colspan=1 rowspan=1 > Family Gravity Coaster 80STD </td><td colspan=1 rowspan=1 > Looney Tunes Seaport </td></tr>
<tr> <td colspan=1 rowspan=1 > Superman: Ultimate Flight </td><td colspan=1 rowspan=1 > Premier Rides </td><td colspan=1 rowspan=1 > 2012 </td><td colspan=1 rowspan=1 > Sky Rocket II </td><td colspan=1 rowspan=1 > DC Universe </td></tr>
<tr> <td colspan=1 rowspan=1 > The Joker </td><td colspan=1 rowspan=1 > Rocky Mountain Construction </td><td colspan=1 rowspan=1 > 2016 </td><td colspan=1 rowspan=1 > I-Box - Custom </td><td colspan=1 rowspan=1 > DC Universe </td></tr>
<tr> <td colspan=1 rowspan=1 > Harley Quinn Crazy Coaster </td><td colspan=1 rowspan=1 > Skyline Attractions </td><td colspan=1 rowspan=1 > 2018 </td><td colspan=1 rowspan=1 > Skywarp </td><td colspan=1 rowspan=1 > DC Universe </td></tr>
</table>
Question:
How many roller coasters were opened at Six Flags Discovery Kingdom in 1998, and what are their names?
Answer:
Six Flags Discovery Kingdom has two roller coasters that were opened in 1998: Kong and Boomerang: Coast to Coaster.