Date of acquisition of property given up

[Account Closed]

My parents owned a commercial building since the 1970s. They added it to their by-pass trust in 1994. My father died in 2000. His half of the building went into the by-pass trust. My mother pass away in 2014. We sold the building in early 2015. Because my dad's half of the building incurred a large capital gains, we did a 1031 exchange. For IRS form 8824 line 3 what is the date of acquisition of the property we gave up? 

The date my parents bought it 1970
The date it went into the trust 1994
The date my dad died 2000
The date my mother died 2014
The date the trust transferred it to the exchange agent 2015.