Select the option that can substitute the bold segment

Solution

"Throw in the towel" means to give up or stop trying, which is synonymous with the idiom "call it a day". Both idioms suggest ending an activity or taking a break after a period of work or effort.

"Give up the ghost" means to stop functioning or cease to exist, typically used for objects, not activities.

"Take the plunge" means to make a bold decision or take a risk, which doesn’t fit the context here.

"Bite the bullet" means to endure something unpleasant, which is also unrelated to stopping work for rest.

Thus, the correct idiomatic replacement for "throw in the towel" is "call it a day".