Question: Who was the dancer at the highest rank at the National Ballet of Canada and American Ballet Theatre?
Context: Carlos Yunior Acosta Quesada CBE (born 2 June 1973) is a Cuban ballet dancer.  He has danced with many companies including the English National Ballet, National Ballet of Cuba, Houston Ballet and American Ballet Theatre.  He has been a permanent member of The Royal Ballet between 1998 and 2015.  In 2003, he was promoted to Principal Guest Artist, a rank which reduced his commitment, enabling him to concentrate on a growing schedule of international guest appearances and tours.  He celebrated his farewell after 17 years at The Royal Ballet, dancing his last performance in November 2015 in "Carmen", which he both choreographed and starred in. Studio Maestro is a ballet school in New York City founded in 1995 by Rose Caiola.  A portion of its students have graduated into ballet companies including American Ballet Theatre, New York City Ballet, Washington Ballet, National Ballet of Croatia, Pennsylvania Ballet, National Ballet of Canada, San Francisco Ballet, Ballet de Espana. Walter Patrick Bissell (December 1, 1957 – December 29, 1987) was an American danseur.  He was a leading principal dancer with the American Ballet Theatre.  On his death at age 30 from a drug overdose, he was described by the artistic director of the American Ballet Theatre Mikhail Baryshnikov as "without a doubt one of the brightest lights in American Ballet Theater's history, or, for that matter, in the entire ballet world".  Bissell was noted for his height and athleticism.  His most famous rôle was as Solor in "La Bayadère".  His death prompted investigations into the alleged widespread drug use within the American Ballet Theatre. The Jacqueline Kennedy Onassis School at American Ballet Theatre (ABT/JKO School) is the associate school of American Ballet Theatre located within the Flatiron District of Manhattan, New York City.  The school comprises a "Children's Division" for ages 4–12, a "Pre-Professional Division" for ages 12–18, and the preparatory program "Studio Company" for ages 16–20.  It was established in 2004 and named in honor of the late, previous First Lady of the United States, Jacqueline Kennedy Onassis, who served on ABT's Board of Trustees as "Honorary Chairman Emerita" for many years prior to her death.  Besides its parent company, graduates of JKO have found employment in various companies, such as National Ballet of Canada, The Royal Ballet, Joffrey Ballet and Dutch National Ballet. Xiomara Reyes is a former principal dancer with American Ballet Theatre.  Born in Cuba, Reyes trained at the Cuban National Ballet School.  After graduation, she danced as a soloist with "La Joven Guardia", an offshoot of Cuba's National Ballet.  After two years, she was invited to perform with the Royal Ballet of Flanders in Belgium and danced with that company for seven years, rising to the rank of first soloist. Aszure Barton was born and raised in Alberta, Canada.  She received her formal training at the National Ballet School in Toronto, where, as a student, she helped originate the ongoing Stephen Godfrey Choreographic Showcase.  To date, she has collaborated with and created works for Mikhail Baryshnikov, Ekaterina Shipulina/Bolshoi Ballet, The National Ballet of Canada, Houston Ballet, American Ballet Theatre, The Martha Graham Dance Company, Nederlands Dans Theater, Sydney Dance Company, Ballet British Columbia, Hubbard Street Dance Chicago, The Juilliard School, and Les Ballets Jazz de Montréal (Resident Choreographer 2005-08), among many others. Martine van Hamel (born 16 November 1945) is a Dutch choreographer, director, teacher, retired ballerina and former Principal dancer at the National Ballet of Canada and American Ballet Theatre (ABT).  She was a gold medalist at the biennial Varna International Ballet Competition, the most prestigious ballet competition in the world, held in Varna, Bulgaria.  She is also a recipient of the Prix de Varna, a recognition rarely awarded, for best artistic interpretation in all categories.  As a dancer, she was one of the leading classical ballerinas in America. A principal dancer (often shortened to principal) is a dancer at the highest rank within a professional dance company, particularly a ballet company. Holly Hynes is an accomplished costume designer with over 250 ballets to her credit, including more than 70 at the New York City Ballet.  Ms. Hynes' designs are also on view in companies around the world, including American Ballet Theatre, San Francisco Ballet, Bolshoi Ballet, National Ballet of Canada, Kirov Ballet, Royal Ballet, Paris Opera Ballet, Royal Danish Ballet, La Scala Theatre Ballet, Koninklijk Ballet van Vlaanderen, Houston Ballet, BalletMet, Pennsylvania Ballet, Ballet Vancouver, Les Grands Ballets Canadiens, American Repertory Ballet, Pacific Northwest Ballet, Atlanta Ballet, Richmond Ballet, Nashville Ballet, Miami City Ballet, Alberta Ballet, Joffrey Ballet, Kansas City Ballet , and the Suzanne Farrell Ballet at The John F. Kennedy Center for the Performing Arts, where she serves as the resident costume designer. Valentina Kozlova (born August 26, 1957) is a Soviet-born Russian American ballerina and founder of Valentina Kozlova International Ballet Competition.  In 1979, while on tour as a young principal dancer with the Bolshoi Ballet, Kozlova defected to the United States, where she became a principal dancer with New York City Ballet and later, opened her own ballet school.  Perhaps best known as a lyrical and expressive ballerina, Kozlova is also renowned as a private coach, producing students who have gone on to garner prestigious prizes and positions in companies such as Boston Ballet, American Ballet Theatre Washington Ballet, Stuttgarter Ballet, Les Ballets Trocadéro de Monte Carlo, Universal Ballet, and the National Ballet of Cuba.
Answer: Martine van Hamel