ANS:D - all the above

Steel bars are generally connected together to achieve greater length than the standard length by providing all of the above types of splices:

1. Straight Bar Splice: Straight bar splices involve aligning the ends of two reinforcement bars and connecting them using mechanical couplers, welded splices, or grouted couplers. This method is commonly used to extend the length of reinforcement bars in situations where continuous reinforcement is required.
2. Hooked Splice: Hooked splices involve bending the ends of reinforcement bars into hooks and then connecting them together by overlapping the hooks and securing them with ties or welds. Hooked splices are often used in reinforced concrete structures where bar bending is feasible and where a standard straight bar splice may not be suitable.
3. Dowel Splice: Dowel splices involve inserting a portion of one reinforcement bar into a corresponding hole or sleeve in another reinforcement bar and then securing them together using mechanical means such as welding, threading, or grouting. Dowel splices are commonly used in applications where a high level of connection strength and alignment accuracy is required, such as in precast concrete construction or in structural steel fabrication.