xin lỗi bn nha, thứ 7 mình mới thi

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.

Farming has come a long way since the days of horse-drawn plows, and now it’s heading swiftly into the twenty-first century. Research at Indiana’s Purdue University uses the Navistar Global Positioning System (GPS) to help increase crop yields and reduce chemical use. GPS uses satellite signals to determine location within inches. Under Purdue’s scheme, a farmer out in the field would use a GPS receiver mounted on his vehicle to pinpoint his position. A computer linked to the receiver and programmed with the field’s soil conditions – which can vary widely from one area to another – would tell the farmer precisely where the plant and how much pesticide and fertilizer to use at that specific site. “Currently the number one cost to the famer is chemicals” say Gary Kurtz, a Professor of Agriculture Engineering at Purdue. Site-specific farming can increase yields while reducing chemical use.

But the cost of this new technology may be too high for the small farmer. The cost of taking and testing soil samples every few feet in a farmer’s field is a limiting factor. Soil tests can run $7 to  $8 each. Mark Morgan, assistant Professor of Agriculture Engineering at Purdue and his graduate assistants are working on a sensor to be attached to the front of a farm implement, enabling the farmer to perform his own soil tests on the go.

The word yields is closest in meaning to _______.

A. conversion

B. formation

C. Breeding

D. performance

Chọn phát biểu đúng

A. C₅H₁₂O có 8 đồng phân thuộc loại ancol  

B. Ancol là hợp chất hữu cơ trong phân tử có nhóm OH-                 

C. Hợp chất C₆H₅-CH₂OH là phenol             

D. C₄H₁₀O có 2 đồng phân ancol bậc 2.

Hoa lưỡng tính và hoa đơn tính bộ phận sinh sản chủ yếu của hoa là nhị và nhụy.

Ví dụ ba loại hoa lưỡng tính là: hoa cải, hoa bưởi, hoa cam; ba loại hoa đơn tính là: hoa mướp, hoa bí, dưa chuột.

x^3 - 5x = y^3 - 5y (1)

x^2 + y^4 = 1 (2) 

Từ (1) => \(x^3-y^3-5x+5y=0\Rightarrow\left(x-y\right)\left(x^2+xy+y^2\right)-5\left(x-y\right)=0\)

=> \(\left(x-y\right)\left(x^2+xy+y^2-5\right)=0\)

=> \(x=y\) hoặc \(x^2+xy+y^2=5\)

(+)  thay x = y vào (2) ta có : \(x^4+x^2=1\)

đặt x^2 = t  (ĐK t>= 0 )pt <=> t^2 + t = 1 

giải ra t 

(+) TH2 :\(x^2+xy+y^2=5\) (3)

ta có : \(x^2+y^4=1\Rightarrow0\le x;y\le1\)