观察下列等式:13+23=32,13+23+33=62,13+23+33+43=102,…,根据上述规律:
(1)第四个等式为( );
(2)第k(k≥1)个等式为( )。
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可以引起颈椎活动受限的情况有()。
A.类风湿关节炎
B.肢端肥大症
C.颈前瘢痕挛缩
D.强直性脊柱炎
E.颈椎损伤
An emergency sea anchor may be constructed by using().
A.a boat bucket
B.an air tank filled with water
C.an oar and canvas weighted down
D.All of the above