Step 1: Analyze the main clause tense.
"The baby kept on crying" is in past tense, so the action in the blank must match in past form.
Step 2: Determine the voice.
The baby is not doing the bathing, it is being bathed → Passive voice is needed.
Step 3: Choose past continuous passive form.
“was being bathed” is the past continuous passive form, matching both tense and voice.
Hence, the correct phrase is “was being bathed.”