Question: Guillermo Varela Olivera spent time on loan to what reserve team that plays in Segunda Division B?

Context paragraphs:
Alacranes Rojos de Apatzingán: Alacranes Rojos de Apatzingán (English: The Red Scorpions ) is a soccer team located in the small city of Apatzingan, Michoacán, Mexico.  The team plays in the Segunda division league, the third tier in the Mexican League System.  The team has competed in the championship finals several times, losing each time.

2016–17 RCD Mallorca season: Real Club Deportivo Mallorca, S.A.D. (Spanish: [reˈal ˈkluβ ðeporˈtiβo maˈʎorka], Catalan: Reial Club Deportiu Mallorca [rəˈjaɫ ˈkɫub dəpoɾˈtiw məˈʎɔɾkə]) is a Spanish football team based in Palma, in the Balearic Islands.  Founded on 5 March 1916 it currently plays in Segunda División, holding home games at the Iberostar Stadium.During the 2016/17 campaign they will be competing in the following competitions: Segunda Division, Copa del Rey.

Louis Robles: Louis Gabriel Robles (born 11 September 1996) is an English-Spanish footballer who plays as a forward for Segunda Division B side Atlético Baleares.

Brentford F.C. Reserves and Academy: Brentford F.C. Reserves was the reserve team of Brentford.  The reserve team played at varying times from 1900 until 2011.  In the Summer of 2012, the English reserve football pyramid and youth system was overhauled under the Elite Player Performance Plan and replaced with a new Academy system and development leagues.  Brentford's reserve team was relaunched as the Brentford Development Squad in 2011 and in 2012 began competing in Professional Development League 2 South.  The club withdrew from the Elite Player Performance Plan and Professional Development League after closing the academy in May 2016 and launched a new Brentford B team.

Guillermo Varela: Guillermo Varela Olivera (] ; born 24 March 1993) is a Uruguayan professional footballer who plays as a right-back for Peñarol.  He began his career with Peñarol, in his home town of Montevideo, before joining Manchester United in 2013.  He spent time on loan to Spanish club Real Madrid's reserve team, Real Madrid Castilla, and at German club Eintracht Frankfurt, before rejoining Peñarol in 2017.

Segunda División B: Segunda División B (English: Second Division B ) is the third level of the Spanish football league system.  It is administered by the RFEF.  It is below the top two levels of the league, the "Primera División" (also known as La Liga) and the "Segunda División", and above the "Tercera División".  The Segunda División B includes the reserve teams of several La Liga and Segunda División teams.

Real Madrid Castilla: Real Madrid Castilla or also known as Real Madrid B is a Spanish football team that plays in Segunda División B.  It is Real Madrid's reserve team.  They play their home games at Alfredo di Stéfano Stadium.

S.C. Braga B: Sporting Clube de Braga B, commonly known as Sporting de Braga B or just Braga B, is a Portuguese football team.  It is the reserve team of S.C. Braga.  Reserve teams in Portugal play in the same league system as the senior team, rather than in a reserve team league.  However, they cannot play in the same division as their senior team, therefore Braga B is ineligible for promotion to the Primeira Liga and also cannot play in the Taça de Portugal and Taça da Liga.

Belgian First Division A: The Belgian First Division A is the top league competition for association football clubs in Belgium.  Following the 2015–16 season it was renamed from the "Belgian Pro League" (officially known as Jupiler Pro League [] ]).  Contested by 16 clubs, it operates on a system of promotion and relegation with the Belgian First Division B.  Seasons run from late July to early May, with teams playing 30 matches each in the regular season, and then entering play-offs 1 or play-offs 2 according to their position in the regular season.  Play-offs 1 (also known as the "title playoffs") are contested by the top 6 clubs in the regular season, with each club playing each other twice.  Play-offs 2 (also known as the "Europa League playoff") are contested by teams ranked 7 to 15 in the regular season, divided in two groups of 6 teams playing each other twice (three teams from the Belgian First Division B also take part in playoff 2).  The team finishing in 16th place is relegated.  s of 2014 the league was sponsored by AB InBev, brewers of Jupiler beer, and officially known as Jupiler Pro League, the sponsor name for the 2016–17 Belgian First Division A is still unknown.

FIBA EuroBasket 2005 Division B: The FIBA EuroBasket 2005 Division B was the first EuroBasket Division B tournament, the lower tier of the EuroBasket Tournament.  At the same time that Division A had the European Championship, division B had a championship to determine which teams would get promoted into division A for the following year.

Supporting paragraphs: Guillermo Varela Real Madrid Castilla
Answer: Real Madrid Castilla