Ở một loài thực vật, gen A quy định thân cao trội hoàn toàn so với alen a quy định thân thấp, gen B quy định quả tròn trội hoàn toàn so với alen b quy định quả dài. Các cặp gen này nằm trên cùng một cặp nhiễm sắc thể. Cây dị hợp tử về 2 cặp gen giao phấn với cây thân thấp, quả tròn thu được đời con phân ly theo tỷ lệ : 31% cây thân cao, quả tròn : 19% cây thân cao, quả dài : 44% cây thân thấp, quả tròn : 6% cây thân thấp, quả dài. Cho biết không có đột biến xảy ra. Tần số hoán vị giữa hai gen nói trên là:

A. 6%

B. 36%

C. 12%

D. 24%

ENGLISH SPEELING

Why does English spelling have a reputation for being difficult? English was first written down when Christian monks came to England in Anglo-Saxon (33) ______. They used the 23 letters of Latin to write down the sounds of Anglo-Saxon speech as they heard it. However, English has a (34) _____ range of basic sounds (over 40) than Latin. The alphabet was too small, and so combinations of letters were needed to express the different sounds. Inevitably, there were inconsistencies in the way that letters were combined.

With the Norman invasion of England, the English language was put at risk. English survived, but the spelling of many English words changed to follow French (35) _____, and many French words were introduced into the language. The result was more irregularity.

When the printing press was invented in the fifteenth century, many early printers of English texts spoke other first languages. They made little effort to respect English spelling. Although one of the shortterm (36) _____ of printing was to produce a number of variant spellings, in the long term it created fixed spellings. People became used to seeing words spelt in the same way. Rules were drawn up, and dictionaries were put together which printers and writers could refer to. However, spoken English was not fixed and continued to change slowly - just as it still does now. Letters that were sounded in the Anglo- Saxon period, like the 'k' in 'knife', now became (37) _____. Also, the pronunciation of vowels then had little in common with how they sound now, but the way they are spelt hasn't changed. No wonder, then, that it is often difficult to see the link between sound and spelling.

Điền vào số (34)

A. longer    

B. deeper     

C. thicker    

D. wider

Cho ba tam giác cân ABC, DBC, EBC có chung đáy BC. Chứng minh ba điểm A, D, E thẳng hàng.