The fisherman cast his net for two whole days but ............... not get a good lot.

Correct option is C

The correct answer is "could" because the sentence refers to an ability or possibility in the past. "Could" is the past tense form of "can" and is used to indicate what the fisherman was able to do (or not do) in the past. The use of "cast" also establishes a past-time context, making "could not" the appropriate choice.
Information Booster
1. "Could" is the past tense of "can," used to show ability or possibility in the past.
2. It is commonly used in negative sentences to denote failure or inability.
3. Words like "but" often indicate a contrast, helping identify the correct tense.
4. Past-time context in the sentence determines the verb form.
5. "Can" would be inappropriate as it denotes present or general ability.
Additional Knowledge
(a) Can: This is used to express ability or possibility in the present or general context. Example: "He can swim well." In the given sentence, "can" is inappropriate as the context is past.
(b) Might: This is used to indicate a possibility, often in hypothetical or less certain situations. It doesn't fit here as the sentence refers to actual events in the past. Example: "He might go to the party if he finishes his work."
(d) May: This is used to express present or future possibility or permission. It is not appropriate here because the sentence refers to past actions. Example: "You may leave early today."