The correct answer is: A. Rounded
Rounded aggregates have the best workability because they pack together more tightly than angular aggregates. This results in a more uniform concrete mix with less voids. Rounded aggregates also flow more easily during placement, which makes it easier to achieve a dense, well-compacted concrete.
Angular aggregates, on the other hand, have more sharp edges and corners. This makes them less likely to pack together tightly, which results in a more porous concrete mix with more voids. Angular aggregates also tend to interlock with each other, which makes them more difficult to place and compact.
As for elongated aggregates, they are somewhere in between rounded and angular aggregates in terms of workability. They pack together more tightly than angular aggregates, but not as tightly as rounded aggregates. They also flow more easily than angular aggregates, but not as easily as rounded aggregates.
In conclusion, rounded aggregates are the preferred shape of aggregate for obtaining the best workability of concrete.