c. The only reason that some people cannot learn a second or foreign language is that they are insufficiently motivated.
TRUE
-it is at some point
Because to what extent does a person go so far for things they love to do?
People learn and adapt things easily if they choose to or simply because they love to do it so learning a foreign language is not as difficult as it seems to be if people actually took time and love to learn and venture to different kinds of culture. because at the end of the day,
Any person can learn or be whatever they want as long as they're happy to do so.
d. All children can learn a second language accent-free.
TRUE- All children have the ability to learn a second language accent-free almost effortlessly. They learn and speak new languages relatively easy and automatically without carrying their native accent characteristic of their region. They can learn more than two langauages without carrying their native accent.
e. No adult can learn a second language accent-free.
FALSE- All adults can learn a second language accent-free because adults have the ability and are capable to learn and speak a second language c without carrying his/her native accent.
f. All human beings have an innate capacity to learn language.
TRUE-The statement is true because according to nativist linguist Noam Chomsky, he claims that children have innate abilities to learn language so-called language acquisition device (LAD). He believes children instinctively learn the language without any formal instruction. Also, he believes that children need to use language non-formal that develops a system of communication to meet their needs and observed that all children make the same errors regardless of the language have learned.

g. Vocabulary is the most important part of learning a second language.
TRUE- Vocabulary is the most important part of learning a second language since it will be the basis to make the skills in reading, speaking, listening and writing a language.
h. Vocabulary is the most difficult part of learning a second language.
FALSE- Though vocabulary is difficult in learning a second language, it all still depends on what language you are learning. There are languages where the vocabulary part is easy to learn but becomes difficult in grammar, listening or pronunciation and vice versa. 
i. Language instruction is a waste of time.
FALSE .Because Language instruction gave us a lot of benefits and one of it is for the benefits of our brain. According to studies in Sweden, language instruction causes areas of the brain associated with memory, namely the cerebral cortex and hippocampus, to increase in size. Like any muscle in the body, regularly exercising your brain can make stronger and more flexible.
j. Learning a second language takes no more time than learning a first language. 
TRUE - according to N. Doidge, "learning a second language, after the critical period language learning has ended, is more difficult because, as we age the more our native language comes to dominate the linguistic map space and the second language finds it hard to compete