HE BUILT _____ HIS COLLECTION OVER A PERIOD OF TEN YEARS.A. IN B....

1. - DE DAP AN KTRA K11 BAI SO 4 HK2
DE DAP AN KTRA K11 BAI SO 4 HK2
1. He built _____ his collection over a period of ten years.a. in b. on c. into d. up