Determine, with proof, which of the following languages are undecidable. That is, for an undecidable language, present a proof via Turing reduction of its undecidability, and for a decidable language, exhibit a decider for that language.

a. LALTERNATE = {.x : neither 00 nor 11 is a substring of x}
b. LEVEN = {(M): L(M) is even}
c. L376-HALT = {((M), 2) : M halts on x in 2|376 steps}
d. LQUICK-HALT = {(M) : There is an input w such that M halts on w within w steps