Final answer:
The word 'deliberately' is the correct answer because it implies a conscious and intentional action. It fits the context of the sentence which describes excluding Glenda from the planning committee to keep the party a surprise.
Step-by-step explanation:
The correct answer is a) deliberately. The correct word to use in the sentence 'We deliberately kept Glenda off the planning committee because we didn't want her to know that the party was to be in her honor.' is deliberately. This word means something done consciously and intentionally. In the context of the sentence, it implies that the action of excluding Glenda from the planning committee was done with the specific intention of keeping the party a surprise for her.
The other options provided do not fit the context of the sentence: 'inadvertently' suggests an action done by accident or without intention, 'intentionally' is synonymous with 'deliberately' and could also be correct, while 'unknowingly' implies a lack of awareness or knowledge about the consequences of the actions. However, since the sentence implies a clear purpose, deliberately is the best choice.