Do I have to use present perfect in the following sentences?
1. The recent research _____ (show) us that the constant misuse or overuse of alcohol may cause cancer of the mouth and throat as well recently.
Question: Do I have to say "has shown" in this sentence? Can I say "shows" in this sentence?
2.As a result, having found that we seldom had a chance to get together, then we decided we would set aside three evenings a week for a sit-down dinner.
Question: Can I say "I found that we seldom had a chance to get together..." in this sentence? Or do I have to use present perfect in the present participle form?
Thank you in advance.