Not less than vs No less than.

[hoangkha]

Hi!
Please help me with this sentence.
1. There were about 100 attendees at the wedding, and ........................ half of them were the bride's and groom's relatives.
A. less
B. not less than
C. no less than
D. nor less than
The key is C but why isn't B chosen?

[Raymott]

Hi!
Please help me with this sentence.
1. There were about 100 attendees at the wedding, and ........................ half of them were the bride's and groom's relatives.
A. less
B. not less than
C. no less than
D. nor less than
The key is C but why isn't B chosen?

B is also possible, but C is much more common in this context.
Whether B is also correct depends on the actual question.