Context: While Old Czech had a basic alphabet from which a general set of orthographical correspondences was drawn, it did not have a standard orthography. It also contained a number of sound clusters which no longer exist; allowing ě (/jɛ/) after soft consonants, which has since shifted to e (/ɛ/), and allowing complex consonant clusters to be pronounced all at once rather than syllabically. A phonological phenomenon, Havlik's law (which began in Proto-Slavic and took various forms in other Slavic languages), appeared in Old Czech; counting backwards from the end of a clause, every odd-numbered yer was vocalized as a vowel, while the other yers disappeared.

Question: What type of orthography did Old Czech lack?
Answer: standard

Question: Why aren't some sound clusters used in modern Czech?
Answer: no longer exist

Question: How did old Czech allow some complex consonant clusters to be pronounced?
Answer: all at once

Question: What type of phenomenon is Havlik's law?
Answer: phonological

Question: Which "yer"s were vocalized as vowels?
Answer: every odd-numbered

Question: What law began in Old Czech?
Answer: Unanswerable

Question: What kind of alphabet was in Proto-Slavic?
Answer: Unanswerable

Question: What did Proto-Slavic have that no longer exists?
Answer: Unanswerable

Question: How did Proto-Slavic let complex consonant clusters to be pronounced?
Answer: Unanswerable

Question: What kind of orthography was missing from Proto-Slavic?
Answer: Unanswerable