Read the following passage and see if you can decide whether to use the singular or the plural form of the words/phrases provided.
...; and you need to find your own balance between talking and listening for each combination of people. In particular, [1a. study has 1b. studies have] shown that men often dominate [2a. discussion 2b. discussions] in which both sexes are involved. Some people don't see asking questions as [3a. an essential part 3b. essential parts] of conversations, so they may need to practise the [4a. skill 4b. skills] of asking questions and genuinely listening.

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