因式分解．

（1）x⁴+x²y²+y⁴

（2）-a²-b²+2ab+4

（3）x⁴+5x²-6

（4）（x+y）（x+y+2xy）+（xy+1）（xy-1）

When you study the local map, you'll find this town is _____.[ ]

A. twice as a large town as that

B. twice the size of that one

C. twice as larger as that one

D. twice as larger a town as that