Final answer:
The piece of double-stranded DNA with 100 base pairs can make 10 complete turns because there are 10 base pairs per turn in the DNA helix.
Step-by-step explanation:
The double-helical structure of DNA consists of two strands wound around each other, with a certain number of base pairs per turn. According to the question, a piece of double-stranded DNA has 100 base pairs. Watson and Crick proposed that there are 10 base pairs per turn in the DNA helix. Since we have 100 base pairs in total, we can calculate the number of complete turns by dividing the total number of base pairs by the number of base pairs per turn (100 ÷ 10 = 10). Therefore, this double helix can make 10 complete turns.