The correct answer is: B. Increase in fineness of cement.
The strength of concrete is a measure of its ability to resist loads. It is affected by a number of factors, including the water-cement ratio, the fineness of cement, the curing time, and the size of aggregate.
The water-cement ratio is the ratio of the weight of water to the weight of cement in a concrete mix. A higher water-cement ratio results in a weaker concrete, while a lower water-cement ratio results in a stronger concrete.
The fineness of cement is a measure of the size of the cement particles. A finer cement will result in a stronger concrete, as the smaller particles will be able to interlock more effectively.
The curing time is the amount of time that concrete is allowed to harden before it is put into use. A longer curing time results in a stronger concrete, as the concrete has more time to develop its strength.
The size of aggregate is the size of the stones or gravel that are used in a concrete mix. A larger aggregate will result in a weaker concrete, as the larger particles will not be able to interlock as effectively.
In conclusion, the strength of concrete increases with an increase in the fineness of cement.