Complex sentence: Luton Hoo was one of the largest houses which for which Adam was wholly responsible, while Adam was working on the mansion the landscape gardener Capability Brown was enlarging and redesigning the park; formerly approximately 300 acres it was now enlarged to 1,200.
Split into simpler sentences: Luton Hoo was one of the largest houses for which Adam was wholly responsible. While Adam was working on the mansion the landscape gardener Capability Brown was enlarging and redesigning the park; formerly approximately 300 acres it was now enlarged to 1,200.