Biện pháp chủ yếu để bảo vệ tài nguyên đất nông nghiệp ở vùng đồng bằng nước ta là

Phần I. Câu trắc nghiệm nhiều phương án lựa chọn. Thí sinh trả lời câu 1 đến câu 18. Mỗi câu hỏi thí sinh chỉ chọn một phương án.

Ở DNA mạch kép, số nucleotide loại A luôn bằng số nucleotide loại T, nguyên nhân là vì

Read the following passage and mark the letter A, B, C, or D to indicate the option that best fits each of the numbered blanks from 18 to 22.

The World’s First GPS

    On a stormy night in 1707, four ships struck rocks off the south coast of England and sank. One thousand, four hundred sailors were drowned. The ships had crashed because they had no way of knowing how far they had travelled in a particular direction; they could not calculate their longitude, which required accurate time measurement. (18) ______. In such difficult circumstances, they believed that the best response to the disaster was a competition: the Longitude Prize.

    The Longitude Prize was no ordinary competition. (19) ______. Geniuses such as Sir Isaac Newton had failed to find a solution, so to ensure the interest of Britain’s greatest scientific minds, the government offered a prize of £20,000 - the equivalent of £2.6 million in today’s money. But to everyone’s surprise, it wasn’t a famous academic who solved the problem, but an unknown carpenter. When John Harrison wasn’t working with wood, (20) ______. An accurate clock would allow sailors to calculate their position, but at the time it was thought impossible to create a mechanical clock (21) ______. The movement of the sea and the changes in temperature destroyed the delicate parts. However, after three frustrated attempts, Harrison’s fourth sea clock, H4, finally triumphed. Its mechanics were so good that the H14 worked better than most clocks on land.

    The Longitude Prize and Harrison’s success (22) ______. However, in 2013, the British government created a new Longitude Prize, offering £10 million to the person who could solve a great challenge to humanity.

(Adapted from Friends Global)

Cho một pin Galvani Zn-Ag, sức điện động chuẩn của pin này là 1,56 V.

Khi nói về phản ứng tổng hợp hạt nhân, phát biểu nào sau đây là sai?

Một chất điểm  M chuyển động đều trên một đường tròn, bán kính R, tốc độ góc $\text{Ω}$. Hình chiếu của  M trên đường kính biến thiên điều hoà có