1. The image below shows the result of an investigation into the effect of two antibiotics, streptomycin and penicillin, on the growth of E. coli bacteria.

Which of the following correctly explain(s) the results of this investigation?

1. Streptomycin and penicillin are drugs that inhibit the growth of bacteria.

2. Exposure to penicillin has caused a mutation to occur in E.coli that has provided the bacteria with penicillin resistance.

3. Random mutation can provide some bacteria with resistance to penicillin.

4. The E. coli colonies are resistant to penicillin but not to streptomycin