Correct the following sentence which has an omitted word.

The mother could not help but at his behaviour.

A. The mother could not help but crying at his behaviour.
B. The mother could not help but cry at his behaviour.
C. The mother could not help but to cry at his behaviour.
D. The mother could not help but cried at his behaviour.
E. The mother could not help was crying at his behaviour.

Choose the correct answer from the options given below:

B only

The correct answer is Option (2) - B only

• The phrase "could not help but" is followed by the base form of the verb (bare infinitive).
• "Cry" is the correct verb form after "could not help but."
• Option A ("crying") is incorrect because "crying" is a gerund, which does not fit this structure.
• Option C ("to cry") is incorrect because "but" should be followed by the bare infinitive, not "to + verb."
• Option D ("cried") is incorrect because "cried" is the past tense form, which is grammatically incorrect in this construction.
• Option E ("was crying") is incorrect because the structure does not require an auxiliary verb.

Thus, the correct sentence is:
"The mother could not help but cry at his behaviour."