I believe the correct answers are:
- an Indo-European language of Germanic origin: this is definitely true as old English (as well as modern English) belongs to the Germanic group of languages, along with Scandinavian languages (Swedish, Norwegian, Danish, Icelandic), German, Yiddish, etc. And all of them are Indo-European languages
- depended on inflections to indicate gender: this statement is also true. Old English, also known as Anglo-Saxon English, used different suffixes to denote the gender of a noun. So if a noun was female, it would have a different suffix from that of male/neuter gender. This has mostly disappeared from modern English.
- depended on inflections to indicate grammatical form: this statement is also true. Old English used different suffixes to denote the form of a word, such as the tense, or possessive form, etc. This is something that modern English has kept as well, and you can see it in -ed suffix for past tense, or 's used for possessive form.
These three options are definitely correct, whereas 'similar to modern English' is definitely incorrect because they almost look nothing alike. I'm not sure about the mixture of many languages though - it had many dialects, but ultimately it was one Germanic/Viking language, so I don't think other languages influenced it a lot at the time - that came later with Middle English.
