what off-spring would result from a High elf mother and a Shadar-kai elf father?

I got into a debate with one of my players they claimed that there character having a full high elf mother and full shadar-kai elf father would be considered a half high-elf and should use the players handbook half elf features and traits. But I disagree and think that it would make them a full elf, either high elf like the mother or shadar-kai like the father. I want the player to stick to only official races for character creation, I just feel that 2 elf sub-races are different enough to make only a half race. What do you think?

What offspring would a High elf mother and a Shadar-kai elf father make? A. Full High elf B. Full Shadar-Kai elf C. Half High elf D. Half Shadar-Kai E. Human

Im trying to stick with the D&D 5E lore.