💡 Detailed Explanation
'Aitsuide' describes a situation where similar events happen in succession without much of a break. It is often used for undesirable things like incidents, accidents, or problems. Choice 1 means "Suspicious incidents are occurring one after another," which is a correct usage. Choice 2 is unnatural for an individual's sequential actions; 'sugu ni' (immediately) would be better. Similarly, for choices 3 and 4, which describe personal actions or reactions, words like 'tsugitsugi to' (one by one) or 'issei ni' (all at once) are more natural.