ýe

Este X bị thủy phân trong dung dịch NaOH, đun nóng theo tỉ lệ khối lượng giữa este và NaOH bằng 17 : 10. Biết X có công thức phân tử C₈H₈O₂, trong phân tử có vòng benzen. Số công thức cấu tạo phù hợp của X là

A. 2.

B. 3.

C. 4.

D. 5.

Đốt cháy hoàn toàn 4,16 gam hỗn hợp X gồm RCOOH và RCOOC₂H₅, thu được 4,256 lít khí CO₂ (đktc) và 2,52 gam H₂O. Mặt khác 2,08 gam hỗn hợp X phản ứng với lượng vừa đủ dung dịch NaOH, thu được 0,46 gam ancol và m gam muối. Giá trị của m là

A. 2,484.

B. 4,70.

C. 2,35.

D. 2,62.

Một lực F →  tác dụng vào đầu M của một thanh có trục quay cố định O (Hình III.8). Đoạn thẳng nào là tay đòn của lực?

A. OM.

B. MN.

C. OI.

D. ON.

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

 Although the “lie detectors” are being used by governments, police departments, and businesses that all want guaranteed ways of detecting the truth, the results are not always accurate. Lie detectors are properly called emotion detectors, for their aim is to measure bodily changes that contradict what a person says. The polygraph machine records changes in heart rate, breathing, blood pressure, and the electrical activity of the skin (galvanic skin response, or GSR). In the first part of the polygraph test, you are electronically connected to the machine and asked a few neutral questions (“What is your name?”, “Where do you live?”). Your physical reactions serve as the standard (baseline) for evaluating what comes next. Then you are asked a few critical questions among the neutral ones (“When did you rob the bank?”). The assumption is that if you are guilty, your body will reveal the truth, even if you try to deny it. Your heart rate, respiration, and GSR will change abruptly as you respond to the incriminating questions.

 That is the theory; but psychologists have found that lie detectors are simply not reliable. Since most physical changes are the same across all emotions, machines cannot tell whether you are feeling guilty, angry, nervous, thrilled, or revved up form an exciting day. Innocent people may be tense and nervous about the whole procedure. They may react physiologically to a certain word (“bank”) not because they robbed it, but because they recently bounced a check. In either case the machine will record a “lie”. The reverse mistake is also common. Some practiced liars can lie without flinching, and others learn to beat the machine by tensing muscles or thinking about an exciting experience during neutral questions.
Question:The word “it” in paragraph 1 refers to ______.

A. the question

B. your body

C. the assumption

D. the truth

Hãy chứng minh các công thức trên và lấy ví dụ minh họa.