Question

This __________ a great matter of concern for him since his childhood. ​

Answer 1

Answer:

Was.

Explanation:

 This was a great matter of concern for him since his childhood.

Here, 'was' is used because of the presence of the word "since". 'Since his childhood' is showing the past nature.

"Was" shows that the subject has been a matter of concern for him, even back in his childhood.

Hope it helps:)