Answer:
a. higher productivity, and another unit of capital would increase output by more than before.
Explanation:
The productivity will be higher as more saving will increase investment.
Therefore, the economy will be more productive as there is more capital per worker.
Is important to comment that due to diminished return theory each additional unit of capital would increase this productivity by a fewer amount. But, this applies on the short run, when the other factors don't change.
Therefore, option a is the correct as the capital increase is not faced agains a bottleneck of the other factor (labor, business and land)