QUES: The key advantage of the four-rail system is that neither running rail carries any current. This scheme was introduced because of the problems of return currents, intended to be carried by the earthed (grounded) running rail, flowing through the iron tunnel linings instead. This can cause electrolytic damage and even arcing if the tunnel segments are not electrically bonded together. The problem was exacerbated because the return current also had a tendency to flow through nearby iron pipes forming the water and gas mains. Some of these, particularly Victorian mains that predated London's underground railways, were not constructed to carry currents and had no adequate electrical bonding between pipe segments. The four-rail system solves the problem. Although the supply has an artificially created earth point, this connection is derived by using resistors which ensures that stray earth currents are kept to manageable levels. Power-only rails can be mounted on strongly insulating ceramic chairs to minimise current leak, but this is not possible for running rails which have to be seated on stronger metal chairs to carry the weight of trains. However, elastomeric rubber pads placed between the rails and chairs can now solve part of the problem by insulating the running rails from the current return should there be a leakage through the running rails.
How did return current effect water and gas in iron pipes?

ANS: water and gas mains

QUES: Modern evolutionary theory continues to develop. Darwin's theory of evolution by natural selection, with its tree-like model of branching common descent, has become the unifying theory of the life sciences. The theory explains the diversity of living organisms and their adaptation to the environment. It makes sense of the geologic record, biogeography, parallels in embryonic development, biological homologies, vestigiality, cladistics, phylogenetics and other fields, with unrivalled explanatory power; it has also become essential to applied sciences such as medicine and agriculture. Despite the scientific consensus, a religion-based political controversy has developed over how evolution is taught in schools, especially in the United States.
In what fields has Darwin's theory of evolution become particularly essential?

ANS: medicine and agriculture

QUES: The placing of the nails in the hands, or the wrists is also uncertain. Some theories suggest that the Greek word cheir (χειρ) for hand includes the wrist and that the Romans were generally trained to place nails through Destot's space (between the capitate and lunate bones) without fracturing any bones. Another theory suggests that the Greek word for hand also includes the forearm and that the nails were placed near the radius and ulna of the forearm. Ropes may have also been used to fasten the hands in addition to the use of nails.
What was the nationality of Destot?

ANS: unanswerable

QUES: The iconic department stores of New Zealand's three major centres are Smith & Caughey's (founded 1880), in New Zealand's most populous city, Auckland; Kirkcaldie & Stains (founded 1863) in the capital, Wellington; and Ballantynes (founded 1854) in New Zealand's second biggest city, Christchurch. These offer high-end and luxury items. Additionally, Arthur Barnett (1903) operates in Dunedin. H & J Smith is a small chain operating throughout Southland with a large flagship store in Invercargill. Farmers is a mid-range national chain of stores (originally a mail-order firm known as Laidlaw Leeds founded in 1909). Historical department stores include DIC. Discount chains include The Warehouse, Kmart Australia, and the now-defunct DEKA.
Where isn't H & J Smith's flagship store?

ANS:
unanswerable