Which one of the following nuclear reactions is a source of energy in the sun?

• A
  $_4^9Be + _2^4He \to _6^{12}C + _0^1n$
• B
  $_1^1H + _1^1H \to _1^2H + _1^0e + \nu$
• C
  $_{56}^{144}Ba + _{36}^{92}Kr \to _{92}^{236}U \to \dots$
• D
  $_1^2H + _1^3H \to _2^4He + _0^1n$