What is the upper bound for a tango tree if k is a number of interleaves?

(a) k+2 O (log (log n))

(b) k O (log n)

(c) K^2 O (log n)

(d) k+1 O (log (log n))

My doubt is from Binary Trees topic in chapter Binary Trees of Data Structures & Algorithms I

This question was posed to me during a job interview.