besides the "splits" people mentioned, also make sure to not fall to "obvious" answer traps. as an example:
What is X?
1) X^2 = 4
2) X >0
This is easy to spot and sometimes easy to select the wrong answer if you are not careful. But there will be harder problems where you still can see an "obvious" answer but you should always try to plug in any values that are 'weird" - Like negatives, fractions, 0 etc. These values almost always weed out the obvious wrong answers like the one above.
Again, you will spot obvious wrong answers much more easier as you do more problems. There are only so many variations of DS questions before they run out.
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