若（2x-1)²⁰¹³＝a₀＋a₁x＋a₂x²＋…＋a₂₀₁₃x²⁰¹³（x∈R），则$\frac{1}{2}$＋$\frac{a_2}{2^2{a}_1}$＋$\frac{a_3}{2^3{a}_1}$+…+$\frac{a_{2013}}{2^{2013}{a}_1}$(     )

“站如松，坐如钟”，青少年如果长期不注意坐立行的正确姿势，骨骼会发生变形，原因是（  ）

“Who needs a shopping mall if you have Taobao?” says Sarah, 28, a writer in Beijing.
Taobao, China’s largest online shopping site, has become an important part in Sarah’s life. She spends lots of money on Taobao.
A growing number of Chinese Internet users like Sarah have found the joys of online shopping. Most online shoppers are students or young workers. More women shop online than men. Clothing and home-use products bought online are the most popular.
It was reported that more than 300 billion yuan was spent on online shopping last year. 80% through Taobao.
Taobao means “looking for treasure” in Chinese. People can find almost everything they need on Taobao, from clothes to books, from candies to DVD players.
You many question the securitv of online shopping. Sarah said, “It’s safe, fast and easy. Unless you receive the products from the sellers and are satisfied with them, the shop owners will not get the money. You can also get your money back if you want to return the products.”

①用头发将蝾螈的受精卵横缢为有核和无核的两半，中间只是很少的细胞质相连，结果无核的一半（a）停止分裂，有核的一半（b）能继续分裂；

②b部分分裂到16～32个细胞时，将一个细胞核挤入到不能分裂的a部分，结果a部分开始分裂、分化，进而发育成胚胎．

下列叙述中，不正确的是（    ）