limestone wrote:Having passed the test for certification, Mackenzie was looking forward to finding a challenging teaching position in her home town.

B. Passing
C. Being that she passed
D. If she had passed
E. For her passing

Will appreciate if anyone can tell the difference between "A" and "B"
[spoiler]OA: A[/spoiler]

Having passed is clear and concise.
"Passing the test for certification", is awkard and confusing.

In addition to being awkward and confusing, B has a verb tense problem. "Passing" is present tense, and although it's used as a modifier (participle) and not a pure verb, it sets up an incorrect timeline - in order to be correct she'd have to have been looking forward specifically while passing the test. It's much more logical that she looked forward after passing the test.

"Having passed" sets up a logical timeline with "was looking" - during the period after which she passed the test, she looked forward to finding a job for which the test qualified her.

One thing that's pretty neat about GMAT grammar is that much of what they test is logic-based...can this modifier logically describe that subject? Do these verbs set up a logical timeline of events? This sentence combines modifier and verb tense logic, so look for opportunities to test your logic on SC questions.