Đặt điện áp xoay chiều u = 200 6 cos ω t V (ω thay đổi được) vào hai đầu đoạn mạch gồm điện trở 100 3  Ω, cuộn cảm thuần và tụ điện mắc nối tiếp. Điều chỉnh ω để cường độ dòng điện hiệu dụng trong đoạn mạch đạt cực đại I m a x . Giá trị của  I m a x  bằng

A. 3 A.

B.  6  A.

C. 2 A.

D.  2 2  A.

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 19 to 28

The term civilization basically means the ___19___ of development at which people live together peacefully in communities. Ancient civilization refers specifically to the first ___20___ and stable communities that became the basis for later states, nations, and empires.

The study of ancient civilization is concerned with the earliest ___21___ of the much broader subject called ancient history. The ___22___ of ancient history began with the invention of writing in about 3100 BC and lasted for more than 35 centuries. Mankind existed long before the written word, but writing made the keeping of a historical record ___23___.

The first ancient societies ___24___ in Mesopotamia and Egypt in the Middle East, in the Indus Valley region of ___25___ are now Pakistan and India, in the Huang He (Yellow River) valley of China, on the island of Crete in the Aegean Sea, and in Central America. All of these civilizations had certain ___26___ in common. They built cities, invented forms of writing, learned to make pottery and use metals, domesticated animals, and created fairly complex social structures with class systems.

___27___ written records and carved inscriptions, the knowledge about ancient peoples is derived from the work of archaeologists. Most of the significant archaeological ___28___ have been made in the past 200 years. The Sumerian culture of Mesopotamia was discovered in the 1890s, and some of the most important archaeological digs in China were made after the late 1970s.

Điền vào ô 25

A. where     

B. which     

C. that 

D. what