Question About Passive & Causatives -2

[tahasozgen]

The Stone Age __ about 21/2 million years ago, when small stones __ into crude chopping tools.


A) had begun / were made
B) began / were made
C) has begun / made
D) began / made
E) was begun / made

Answer key depicts B. My answer is A.

action 1: the beginning of the stone age .
action 2: small stones were made into crude chopping tools.

According to my reasoning, since action 1 starts before action 2, answer A should be answer. Why my answer is wrong? Thanks in advance.

[jutfrank]

Action 1 does not start before action 2. They happened at the same time. The point is that they are the same event. The time when stones first started to be made into crude tools is what we call the Stone Age.

B) is the correct answer.