Which one is wrong in grammar?

Ever since the Internet ? has become part of our daily lives, online shopping has been getting more popular. It is convenient and it saves time and money. In order to be a smart consumer, you should educate ? yourself on how to shop online. The following suggestions will help you ? shop wisely. Check the product reviews on shopping sites. This is especially recommended when you are intending to purchase an expensive product. You can check ? whether there have been any complaints about the product. For example, here are two reviews of the same product. Each of them ? shows different points of view.

Q: Which one is wrong in grammar?

The answer is d but I think that 'check whether...' is acceptable and correct in grammar. What do you native English speakers think? And if I chose one answer, I would choose a because since is usually compatible with past tense, isn't it? What do you native English speakers think?

Thank you so much as usual!