Correct Answer: inarticulate

Solution : The fourth option is the correct choice.

In the sentence, Howard attempted to speak, but the only sound that he produced was an indistinct, squeaky gargle. The use of inarticulate appropriately characterises the quality of Howard's speech at that moment. Inarticulate denotes being unable to express oneself clearly.

The meanings of the other options are as follows:

• Implausible: It denotes not seeming reasonable or probable.
• Sincere: It denotes a person, feeling, or expression that is free from pretence or deceit.
• Easy: It denotes something requiring no great labour or effort.