The New Testament Quotes the Greek

This one is measurable, and the numbers are striking.
Scholars have compared every Old Testament quotation in the New Testament against both the Masoretic Text and the Septuagint. About twenty percent of the time MT and LXX agree, so the quotation tells you nothing about which was used.
In the other eighty percent - where they disagree - "the New Testament reading agrees with the MT less than five percent of the time."
Less than five percent. Which means that when the apostles had a choice between the Hebrew tradition behind our Old Testament and the Greek translation, they overwhelmingly quoted the Greek.
You can see it without knowing the languages. Hebrews 10:5 has "a body you have prepared for me" - that is the Septuagint of Psalm 40. The Hebrew reads "ears you have dug for me."
Scripture links:
- Hebrews 10:5-7 - "a body have you prepared for me."
- Psalm 40:6 - "you have given me an open ear."
- Hebrews 1:6 - "let all God's angels worship him."
- Acts 15:16-18 - James quotes Amos in its Greek form.
The apostles' working Bible was the Greek one.