The pronoun ‘it’ can be used where the subject is unclear at C1, and verbs such as ‘conclude’ are only used by C1 learners. For example:
However, this post is about reporting with modal verbs.
C1 point 208 in MODALITY is defined as:
‘can’ in passive reporting clauses in a more formal impersonal style (e.g. for reports and academic contexts), such as ‘It can be said that’, ‘It can be argued (that)’, ‘It can be concluded that’, ‘It can be considered”
This is similar to the B2 English Vocabulary Profile point: ‘BE + said to’ which means
many people believe something about something
Also, the modal + passive form in a range of contexts is also B2, or is the following example impersonal enough to be C1?
*’could’ should also be accepted under this point as C1 complexity. For example:
A search in iWeb for:
It_P can be argued|said|argued|concluded|considered
1 IT CAN BE SAID 5184
*The following example is not really ‘impersonal’ knowledge.
2 IT CAN BE ARGUED 4337
3 IT CAN BE CONSIDERED 2497
4 IT CAN BE CONCLUDED 1300