💡 Detailed Explanation
The correct answer is 「ざるを得ない」 (zaru o enai), which means 'to have no choice but to do something' or 'cannot avoid doing something', often against one's will. It's formed with the nai-stem of the verb (e.g., 引き受ける -> 引き受け -> 引き受けざるを得ない). 「かねない」 (kanenai) means 'might do something bad'. 「ようがない」 (you ga nai) means 'there is no way to do something'. 「わけにはいかない」 (wake ni wa ikanai) means 'cannot do something for social or moral reasons', but it's usually used when the speaker wants to do it but can't, or feels an obligation not to do it. Here, the obligation is to do it.