'Not until three years ago _________ to work outside.' [(a) he began (b) he begins (c) began he (d) did he begin ]

Question

'Not until three years ago _________ to work outside.'

[(a) he began (b) he begins (c) began he (d) did he begin ]

Hi guys, I know the answer to this question is 'd', but I've had someone ask me the dreaded question: 'why?'

Can anyone help me to explain this? The student wants to know - why not answer 'a'?

Thank you so much.

Answer 1

It's a negative sentence so it requires do/did. Consider the following two sentences:

• He began to work outside.
• He did not begin to work outside.

Similarly,

• Three years ago, he began to work outside.
• Three years ago, he did not begin to work outside.
• Until three years ago, he did not begin to work outside.
• Not until three years ago, did he begin to work outside.