The English language is terribly ambiguous... even for native speakers. Unfortunately, test creators frequently do not appreciate this fact (a crowd sourced question review service for teachers and exam creators might be an interesting solution). One of my favorite examples is the number of alternate scenarios that this sentence could be describing:

  the boy saw a mouse running in his pajamas

Counter-point: Throughout school, I often pondered whether the ambiguity in test questions was actually intentional. In the real world, you are often given problems to solve that are poorly defined, so perhaps this is good preparation? However, when working on real world problems, you can clearly state any assumptions you've made to arrive at your solution and this is not easily applied to answering questions on a bubble sheet test with very limited context.