The blanks in the proof is as follows
Blank 1 is given
Blank 2 is: HL congruence theorem
Blank 3 is: CPCTC
What is CPCTC?
CPCTC stands for Corresponding Parts of Congruent Triangles are Congruent
The CPCTC theorem says that if two triangles are proven to be congruent, then their corresponding parts (sides and angles) are also congruent.
With this theorem, we can say that AC is congruent to BD