Final answer:
During metaphase I of meiosis, each chromosome pairs with its homolog to form a bivalent, comprising four chromatids. Thus, if there were 20 chromosomes after meiosis II, there would have been 80 chromatids during metaphase I.
Step-by-step explanation:
If a cell contains 20 chromosomes immediately after completion of telophase of meiosis II, it indicates that the cell has gone through the process of meiosis which reduces the chromosome number by half. Therefore, in that cell, there would have been 40 chromosomes at the start of meiosis I (since the cell ends with half that number).
During metaphase I, each chromosome aligns with its homologous partner, and each pair is referred to as a bivalent or tetrad, which contains four chromatids. Thus, if there are 20 bivalent chromosomes during metaphase I, there would be 80 chromatids present (20 bivalents times four chromatids per bivalent). Therefore, the correct answer to the question 'How many chromatids were present in metaphase I?' given that there were 20 chromosomes after meiosis II, is 80, which is option d).