Read the following passage carefully and then choose the best answer to  each question.

As heart disease continues to be the number-one killer in the United States, researchers have become increasingly interested in identifying the potential risk factors that trigger heart attacks. High-fat diets and "life in the fast lane" have long been known to contribute to the high incidence of heart failure. But according to new studies, the list of risk factors may be significantly longer and quite surprising.

          Heart failure, for example, appears to have seasonal and temporal patterns. A higher percentage of heart attacks occur in cold weather, and more people experience heart failure on Monday than on any other day of the week. In addition, people are more susceptible to heart attacks in the first few hours after waking. Cardiologists first observed this morning phenomenon in the mid-1980, and have since discovered a number of possible causes. An early-morning rise in blood pressure, heart rate, and concentration of heart stimulating hormones, plus a reduction of blood flow to the heart, may all contribute to the higher incidence of heart attacks between the hours of 8:00 A.M. and 10:00 A.M.

           In other studies, both birthdays and bachelorhood have been implicated as risk factors. Statistics reveal that heart attack rates increase significantly for both females and males in the few days immediately preceding and following their birthdays. And unmarried men are more at risk for heart attacks than their married counterparts. Though stress is thought to be linked in some way to all of the aforementioned risk factors, intense research continues in the hope of further comprehending why and how heart failure is triggered.

What does the passage mainly discuss?

A. seasonal and temporal patterns of heart attacks                

B. cardiology in the 1980s

C. risk factors in heart attacks                                       

D. diet and stress as factors in heart attacks

The Spratly Islands and the Paracel Islands _______ Vietnam

A. stand for 

B. name after 

C. consist of 

D. belong to

Este CH₂=CHCOOCH₃ không tác dụng với

A. H₂O (xúc tác H₂SO₄ loãng, đun nóng).

B. H₂ (xúc tác Ni, đun nóng).

C. kim loại Na.

D. dung dịch NaOH, đun nóng.

Câu 4 nek:

Mùa xuân năm 544, Lý Bí lên ngôi Hoàng đế, đặt tên nước là Vạn Xuân, đóng đô ở cửa sông Tô Lịch (Hà Nội), đặt niên hiệu là Thiên Đức, lập triều đình với hai
ban văn, võ.

Có ý nghĩa là: Ko bik

Đốt cháy hoàn toàn 0,15 mol este thu được 19,8 gam CO₂ và 0,45 mol H₂O. Công thức phân tử của este là:

A. C₂H₄O₂

B. C₃H₆O₂

C. C₄H₈O₂

D. C₅H₁₀O₂