The verb 'lean' is a synonym for the verb 'trend'. And for the synonym to 'hypothesis', the term 'suggestion' is most appropriate because both are proposed explanations or ideas put forward for consideration.
In the context of this question, when we look at the word trend as a verb, it generally means to change or to veer in a certain direction. Among the provided options, the word lean is the most appropriate synonym. When used as a verb, to lean can mean to incline towards a particular direction or point of view, which is similar to how trend can mean to develop in a general direction.
For the second part of your question regarding a synonym for a hypothesis, a hypothesis is best defined as a proposed explanation made on the basis of limited evidence as a starting point for further investigation. Therefore, the word suggestion (d) is the closest in meaning, because like a hypothesis, a suggestion is something that is put forward for consideration.