By the time we reach the point where it says “have been shown to be neutral” we know that
SVA is being tested here. Based on this we can quickly
eliminate Option A. We are then left with:
B –
Even though the impact of DST,
at the onset of which clocks are set forward by an hour, has been shown to be neutral, at best—
research indicates that it actually increases the number of car accidents occurring on the Monday after the clocks spring forward—some countries do not observe it.
Look at these sentences with ‘even though’:
I bought the video game,
even though it was expensive.
Even though his car wasn’t in perfect shape, Jake still won the race.
The use of ‘even though’ in this question does not satisfy the above structure. There is no contradiction or contrast that follows the use of ‘even though’. The negative effect that is given (increase in the number of accidents) is not used here as contrast but as a reason why some countries don’t observe it. We can eliminate this.
C –
Since the impact of DST,
at the onset of which clocks are set forward by an hour, has been shown to be neutral, at best—
research indicates that it actually increases the number of car accidents occurring on the Monday after the clocks spring forward—some countries do not observe it.
C is to the point. Since impact of DST is neutral at best or negative, some countries do not follow it. This is the right answer.
D –
Because the impact of DST,
at the onset of which clocks are set forward by an hour, has been shown to be neutral
—at best, research indicates that it may actually result in an increase in the number of car accidents occurring on the Monday after the clocks spring forward—some countries do not observe it.
Here the structure is not what is required. It changes the intended meaning. We need the phrase to say: neutral, at best (and not neutral—at best,). We can eliminate this option.
E –
Because DST,
at the onset of which clocks are set forward by an hour, has been shown to have a neutral impact, at best—
research indicates that it may actually result in a possible increase in the number of car accidents occurring on the Monday after the clocks spring forward—some countries do not observe it.
Redundancy – ‘may’ and ‘possible’ together. Eliminate this option.
Hope this helps.