Question

By this light he could see her moving to and fro ,preparing Tom's supper (use -be able to)​

Answer 1

Answer:

was able to see

Explanation:

• Words such as Be able to, can, could are often used to talk about the ability, possibility or awareness of someone.

• Can or could are modal auxiliary verbs used to talk about the ability to do something in the present or past tense respectively.

• 'To be able to' is not a modal auxiliary and is used to refer to the same in a formal way.
• We can say it is the conjugated verb ('to be')+ adverb(able)+the infinitive (to).

• "Be able to" with stative verbs such as see, hear, feel, and taste is used to discuss or express ability related to a single incident in the past.

• The given sentence describes an incident in the past, hence be able to should be used with the action verb.

Hence the correct sentence is

By this light, he was able to see her moving to and fro, preparing Tom's supper.