QUES: In the example above, the identity and the rotations constitute a subgroup R = {id, r1, r2, r3}, highlighted in red in the group table above: any two rotations composed are still a rotation, and a rotation can be undone by (i.e. is inverse to) the complementary rotations 270 for 90, 180 for 180, and 90 for 270 (note that rotation in the opposite direction is not defined). The subgroup test is a necessary and sufficient condition for a subset H of a group G to be a subgroup: it is sufficient to check that g1h H for all elements g, h H. Knowing the subgroups is important in understanding the group as a whole.d["]

What rotation can a rotation be reversed by?
What is the answer?
ANS: inverse
QUES: Arsenal was the first club from the south of England to join The Football League, in 1893. They entered the First Division in 1904, and have since accumulated the second most points. Relegated only once, in 1913, they continue the longest streak in the top division. In the 1930s, Arsenal won five League Championships and two FA Cups, and another FA Cup and two Championships after the war. In 197071, they won their first League and FA Cup Double. Between 1988 and 2005, they won five League titles and five FA Cups, including two more Doubles. They completed the 20th century with the highest average league position.

In what year did Arsenal qualify to be in the First Division?
What is the answer?
ANS: 1904
QUES: The terms asphalt and bitumen are often used interchangeably to mean both natural and manufactured forms of the substance. In American English, asphalt (or asphalt cement) is the carefully refined residue from the distillation process of selected crude oils. Outside the United States, the product is often called bitumen. Geologists often prefer the term bitumen. Common usage often refers to various forms of asphalt/bitumen as "tar", such as at the La Brea Tar Pits. Another archaic term for asphalt/bitumen is "pitch".

What is the substance usually called outside of the La Brea Tar Pits?
What is the answer?
ANS:
unanswerable