Complex sentence: This force also penetrated deep behind the Abucay-Mauban Line along the Abo-Abo River Valley, but their advance was held up by combined units of the 21st and 51st divisions, the 31st Division of BGen.
Split into simpler sentences: This force also penetrated deep behind the Abucay-Mauban line along the Abo-Abo river valley. But their advance was held up by combined units of the 21st and 51st Divisions, the 31st Division of BGen.