Here's a short story:

(CNN) -- The Williams sisters have not had it easy in recent years. Two of the modern era's most successful women tennis players have been beset by health problems which have deprived the game of two of its most marketable stars. 

Serena has overcome life-threatening blood clots on both lungs, while older sibling Venus is this week making her long-awaited WTA Tour comeback as she battles a debilitating illness that has sidelined her since last year's U.S. Open. 

After pulling out of her second-round match in New York, Venus revealed she had been diagnosed with Sjogren's syndrome -- an incurable condition which affects energy levels and causes pain in the joints. 

"I just didn't feel well before my second-round match, to the point where I couldn't play," the 31-year-old told CNN's Connect the World show. 

"At the beginning of the tournament, I wasn't sure how far I would get or what I would do, I was kind of living on a hope and a dream." 

After a glittering 18-year professional career which has seen her become the first black woman to be ranked world No. 1 in the Open era, winning seven grand slam singles titles and 12 major doubles crowns alongside Serena, Williams would have been forgiven for deciding to chuck in the towel. 

But, instead of eying an early retirement, the winner of three Olympic gold medals set her sights on managing her illness and returning to the baseline ahead of this year's London Games. 

"When you don't feel well and things are taken away from you, it's hard to stay positive," the former world No. 1 said. "But, for me, it is not an option to get negative or to feel sorry for myself.  (End of story)

Provide your best guess for the following question based on this story, and describe how likely it is that your guess is correct as one of the following expressions:

Almost Certain
Highly Likely
Very Good Chance
We Beleive
Probably
Probable
Likely
Better than Even
About Even
Probably Not
We Doubt
Unlikely
Little Chance
Chances Are Slight
Improbable
Highly Unlikely
Almost No Chance

Give ONLY the guess and your confidence, no other words or explanation. For example:

Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>
Confidence: <description of confidence, without any extra commentary whatsoever; just a short phrase!>

Here are a few examples of questions and answers:

Question: What illness does Venus have?
Guess: Sjogren's syndrome
Confidence: <appropriate level of confidence in this guess>

Question: how many grand slam single titles has she won?
Guess: seven
Confidence: <appropriate level of confidence in this guess>

Question: what did Serena suffer from?
Guess: life-threatening blood clots on both lungs
Confidence: <appropriate level of confidence in this guess>

Question: how old is Venus?
Guess: 31
Confidence: <appropriate level of confidence in this guess>

Now answer the following question in the same format.

Question: what do they play?

tennis