Which of the following could be used to build suspense in a story?
repetition of words that makes the reader confused
short phrases that make the reader interested
words that make the reader think
punctuation that makes the reader pause

The correct answer is: Short phrases that make the reader interested.

Some authors recommend  the use of short sentences as the genre requires variety and flow to avoid repetition and boredom. In this way the pace of the reading is increased keeping the reader's attention. I read an example that was very helpful, imagine someone that is anxious or scared, when he sepaks he uses few words at a time, forming complex sentences turns difficult. By writing with short sentences you can be able to transmit this kind of emotions in a more effective way. Remember that suspense's objective is to make the reader wonder at all time if the protagonist will overcome  the problems presented, the reader must frecuently face uncertainty.

B) Short phrases that make the reader interested

it's either a or b. i'm leaning more towards a.