Kim Hyun-sik (January 7 1958 – November 1, 1990) was a musician in South Korea, active during the 1980s.
 He debuted in 1980, releasing his first album, "Spring, Summer, Fall, Winter", along with his band of the same name.
 He died at the age of 32 from cirrhosis.
 He is considered one of the most popular and notable musicians of the 1980s in Korea, well-known for his unique, husky, emotional vocal style.
 Kim released five albums while alive, with his sixth album—"Kim Hyun-sik VI", popularly known by the title of its lead single "My Love By My Side"—being released posthumously.
 Kim broke out of the hospital to finish the vocal recordings for his last album, showing his dedication to his profession.
 He won the Disc Daesang (Album of the Year) award at the 1991 Golden Disc Awards, the Korean approximation of the Grammy Awards, for his posthumous sixth album, "Kim Hyun-sik VI".
 Kim was also honored by having two episodes of the popular singing competition show "Immortal Songs 2" dedicated to his music.
Optometry is a health care profession which involves examining the eyes and applicable visual systems for defects or abnormalities as well as the medical diagnosis and management of eye disease.
 Traditionally, the field of optometry began with the primary focus of correcting refractive error through the use of spectacles.
 Modern day optometry, however, has evolved through time so that the education curriculum additionally includes intensive medical training in the diagnosis and management of ocular disease in countries where the profession is established and regulated.
 Optometrists (also known as Doctors of Optometry in the US and Canada for those holding the O.D. degree or Ophthalmic Opticians in the UK) are medical professionals who provide primary eyecare through comprehensive eye examinations to detect and treat various visual abnormalities and eye diseases.
 Being a regulated profession, an optometrist's scope of practice may differ depending on the location.
 Thus, disorders or diseases detected outside the treatment scope of optometry are referred out to relevant medical professionals for proper care, more commonly to ophthalmologists who are physicians that specialize in tertiary medical and surgical care of the eye.
 Optometrists typically work closely together with other eye care professionals such as ophthalmologists and opticians to deliver quality and efficient eyecare to the general public.
Mind Control is the fourth album by American post-grunge band Tantric and was released on August 4, 2009.
 It is the band's second album under Silent Majority Group and was produced by Brett Hestla, marking Tantric's departure from mainstay producer Toby Wright.
 "Mind Control" retains the band's 2008 lineup with the exception of drummer Kevin Miller who was replaced by Richie Monica.
Dark New Day, formerly known as "Dark Blue", was an American hard rock supergroup formed in 2004 featuring Brett Hestla of Virgos Merlot, Clint Lowery of Sevendust, Troy McLawhorn of DoubleDrive, Corey Lowery of Stereomud and Stuck Mojo, and Will Hunt of Skrape.
 Their debut album, "Twelve Year Silence", was released in 2005, followed by the EP "Black Porch (Acoustic Sessions)" in 2006.
 Though still inactive, Dark New Day released their second album, titled "New Tradition", in 2012.
 On February 19, 2013, the band released their third album, titled "Hail Mary".
Kim Jung-ah (born August 2, 1983), better known by the mononym Jung Ah or Jung A, is a South Korean singer.
 She was a member of Kiss Five and graduated member of After School.
 In 2016, Pledis Entertainment announced that her contract had expired and she had graduated from After School naturally.
An apprenticeship is a system of training a new generation of practitioners of a trade or profession with on-the-job training and often some accompanying study (classroom work and reading).
 Apprenticeship also enables practitioners to gain a license to practice in a regulated profession.
 Most of their training is done while working for an employer who helps the apprentices learn their trade or profession, in exchange for their continued labor for an agreed period after they have achieved measurable competencies.
 Apprenticeships typically last 3 to 7 years.
 People who successfully complete an apprenticeship reach the "journeyman" or professional certification level of competence.
Brett Adam Hestla, (born February 4, 1973), is an American musician and record producer.
Mirror of the Witch () is a South Korean television series starring Yoon Shi-yoon, Kim Sae-ron, Lee Sung-jae, Yum Jung-ah and Kwak Si-yang.
 The story of the drama is inspired by the book "Dongui Bogam".
 It replaced "Ms. Temper and Nam Jung-Gi" and aired on cable network JTBC on Fridays and Saturdays at 20:30 (KST) for 20 episodes from May 13, 2016 to July 16, 2016
Model () is a 1997 South Korean television series starring Kim Nam-joo, Han Jae-suk, Jang Dong-gun and Yum Jung-ah.
 It aired on SBS from April 9 to August 7, 1997 on Wednesdays and Thursdays at 21:45 for 36 episodes.
The Secret of My Love (Hangul: 내 남자의 비밀 ; RR: "Nae Namjaeui Bimil "; lit.
 My Man's Secret ) is a 2017 South Korean television series starring Song Chang-eui, Kang Se-jung, Kim Da-hyun, and Park Jung-ah.
 The series airs on KBS2 on Monday to Friday from 7:50 p.m. to 8:30 p.m. (KST).

Question: Kim Jung-ah and Brett Hestla both work under which profession?
Answer: musician