Which of the following statements is/are correct with regard to disadvantages of GM crops?

Question

$\begin{array}{1 1} \text{a. GM crops can affect the human health by causing allergic reactions.} \\ \text{b. Transgenes in commercial crops can endanger native species.}\\ \text{Example: The Bt. Toxin gene expressed in pollen might endanger pollinators like honey bees.} \\ \text{c. Production of GM crops cause damage to the natural environment and is always costly.} \\ \text{d. All of these.} \end{array}$