Concept:The phrasal verb "chip in" means to contribute money or help with a task, and it fits all three sentences correctly.
Explanation:The underlined phrases "crack up", "check through", and "check with" are all incorrect in their given contexts.
The single phrasal verb that can replace all of them is "chip in".
In sentence 1: "We will chip in to pay his bills" means we will contribute money to pay his bills.
In sentence 2: "I will chip in to collect money for the campaign" means I will help in collecting the money.
In sentence 3: "He will chip in to serve the meal" means he will help in serving the meal.
Hence, "chip in" works perfectly in all three sentences.
The other options are rejected because:
"Came across" means discovered by accident, as in "I came across an old book."
"Come apart" means to separate into pieces, as in "The chair will come apart."
"Fall out" means to stop being friends after a disagreement, as in "They fell out over money."
None of these options fits the meaning of all three sentences.
Answer:Option B — "Chip in"