Question: What form of entertainment are Martha and Königskinder both performed?

Context paragraphs:
Moment Rustica (ballet): Moment Rustica was a Martha Graham ballet performed to the music of Francis Poulenc.  It premiered on April 14, 1929 at the Booth Theater in New York City.  The performance marked the debut of Graham's concert ensemble, Martha Graham and Group, the predecessor of the Martha Graham Dance Company.

Horizons (ballet): Horizons was a modern dance work choreographed by Martha Graham to music by Louis Horst with a set designed by Alexander Calder.  It premiered on February 23, 1936, at the Guild Theatre in New York City.  "Horizons" was divided into four parts, two ensemble dances and two solos: "Migration: New Trails" (ensemble), "Dominion: Sanctified Power" (solo), "Building Motif: Homesteading" (solo) and "Dance of Rejoycing" (ensemble).  The ballet was performed by Martha Graham and Group, the predecessor of the Martha Graham Dance Company.

Königskinder: Königskinder (German for "The King's Children") is a stage work by Engelbert Humperdinck that exists in two versions: as a melodrama and as an opera or more precisely a "Märchenoper".  The libretto was written by Ernst Rosmer (pen name of Else Bernstein-Porges), adapted from her play of the same name.

William Koger House (Smithsonia, Alabama): The William Koger House is a historic residence near Smithsonia, Alabama.  The house was built around 1830 by William and Martha Koger, planters from Virginia.  The Kogers brought their native architectural form, the Tidewater-type cottage, with them to North Alabama.  The house was the center of a 630-acre (255-ha) plantation, which included an island in the Tennessee River.  After William's death, Martha continued to manage the farm until her death in 1892.

Mary of Bethany: Mary of Bethany (Judeo-Aramaic מרים, "Maryām", rendered Μαρία, Maria, in the Koine Greek of the New Testament; form of Hebrew מִרְיָם, Miryām, or Miriam, "wished for child", "bitter" or "rebellious") is a biblical figure described in the Gospels of John and Luke in the Christian New Testament.  Together with her siblings Lazarus and Martha, she is described by John as living in the village of Bethany near Jerusalem; in Luke only the two sisters, living in an unnamed village, are mentioned.  Most Christian commentators have been ready to assume that the two sets of sisters named as Mary and Martha are the same, though this is not conclusively stated in the Gospels, and the proliferation of New Testament "Marys" is notorious.

Course (ballet): Course was a modern dance work choreographed by Martha Graham to music by George Antheil.  The piece sometimes appeared on programs as "Course: One in Red; Three in Green; Two in Blue; Two in Red".  It premiered on February 10, 1935, at the Guild Theatre in New York City.  The ballet was performed by Martha Graham and Group, the forerunner to the Martha Graham Dance Company.

Young Martha: Young Martha is a collaborative extended play by American rapper Young Thug and producer Carnage.  The EP was released on September 22, 2017, by YSL, 300 Entertainment and Heavyweight Records.  "Young Martha" includes four tracks and guest appearances from Meek Mill and Shakka.  It was produced by Carnage along with co-production from OG Parker, Felix Snow and Wheezy.

Martha (opera): Martha, oder Der Markt zu Richmond ("Martha, or The Market at Richmond") is a "romantic comic" opera in four acts by Friedrich von Flotow set to a German libretto by Friedrich Wilhelm Riese and based on a story by Jules-Henri Vernoy de Saint-Georges.

Abba b. Martha: Abba b. Martha was a Babylonian scholar of the end of the third century and beginning of the fourth.  He seems to have been in poor circumstances.  Once he incurred a debt to the resh galuta (exilarch), which he could not repay, and only by disguising himself did he at the time escape arrest for it.  Later he was apprehended and sorely pressed for payment; but when the exilarch discovered that his debtor was a rabbinical scholar, he released him.  His mother, Martha, seems to have been in easy circumstances; for, when Abba was bitten by a rabid dog and, in accordance with contemporary therapeutics, was obliged to drink through a tube of copper, Martha substituted one of gold.  Notwithstanding his pecuniary straits, Abba did not take advantage of the Biblical and Talmudic law, according to which the Sabbatical year cancels all debts.  He once owed some money to Rabbah, and paid it in the year of release, using the form of a donation.

Martha's Son: Martha's Son (7 May 1987 – May 1999) was a British Thoroughbred racehorse who competed under National Hunt rules.  After competing in minor hurdle events for the first two years of his racing career, he demonstrated dramatic improvement when switched to steeplechasing, winning nine consecutive races including the Peterborough Chase, Victor Chandler Chase and Comet Chase.  He returned after a long injury lay-off to produce his best form as a ten-year-old in the spring of 1997, defeating strong fields in both the Queen Mother Champion Chase and the Melling Chase.  His veteran trainer Tim Forster regarded him as the best horse he had ever trained.  Martha's Son was retired from racing after failing to recover from serious muscular injuries in a race in November 1997.  He died in May 1999.

Supporting paragraphs: Martha (opera) Königskinder
Answer: opera