Stars have been significant features in the design of many United Stat

Stars have been significant features in the design of many United States coins and THEIR number has varied from one to forty-eight stars. Most of the coins issued from about 1799 to the early years of the twentieth century bore thirteen stars representing the thirteen original colonies. 
CURIOUSLY ENOUGH, the first American silver coins, issued in 1794, had fifteen stars because by that time Vermont and Kentucky have joined the Union. At that time it was apparently the intention of mint officials to add a star for each new 
state. Following the admission of Tennessee in 1796, for example, some varieties of half dimes, dimes, and half dollars were produced with sixteen stars. 
 As more states were admitted to the Union, however, it quickly became apparent that this scheme would not prove practical and the coins from 1798 were issued with only thirteen Stars - one for each of the original colonies. Due to an error at the mint, one variety of the 1828 half-cent was issued with only twelve stars. There is also a variety of the large cent with only 12 stars, but this is the result of a die break and is not a true error. 

The word "their" in line 1 refers to _________. 

• A. A. features
• B. B. coins
• C. C. stars
• D. D. colonies

Từ “their” trong dòng 1 đề cấp đến _________. 
A. features: đặc điểm 
B. coins: đồng xu 
C. stars: ngôi sao 
D. colonies: thuộc địa 
Thông tin: Stars have been significant features in the design of many United States coins and their number has varied from one to forty-eight stars. 
Tạm dịch: Các ngôi sao là đặc điểm quan trọng trong thiết kế của nhiều đồng tiền Hoa Kỳ và số lượng của chúng thay đổi từ một đến bốn mươi tám sao. 
=> their number = the number of stars (số lượng ngôi sao)