задание по англ. языку

определите в следующих предложениях видовременные формы глаголов:
1. the calf receives colostrum, the mammary secretion PRODUCED by the cow immediately following parturition.(participle II?)
2. though some cows have LIVED 17 years or more, the average cow is culled or dies between five and six years of age.
3. a deficiency of niacin WAS one of the causative factors in pellagra. (past simple?)
4. popular scientists WERE WORKING there for some period of time.
глаголы нашла. не знаю правильно или нет. не могу разобраться с формами